Animal proteins have certain advantages, especially for the younger men out there. And supplement manufacturers and bodybuilding magazines push egg, whey and casein proteins very heavily for reasons that are well-known and well-understood by most men interested in athletics and/or bodybuilding. In this article I want to go into the reasons that a man might want to actually to back off of animal protein and instead lean more heavily on plant based proteins.
Below are Five Reasons to Consume Plant Based Proteins:
1. Potential Anti-Aging. Animal proteins are stimulatory and the primary reason is that they are heavy in the sulfur-based amino acid methionine. Methionine basically triggers an extra release of IGF-1, which stands for Insulin-Like Growth Factor. It ain't called "growth factor" for nothing and basically prods the body into cell turnover and production. When you are young, you want lots of growth factors in order to maximize one's size and development. Past the age of about 35, this is no longer needed and IGF-1 can cause growth in things like cancer nodules and tumors. Plus, as its name implies, IGF-1 also mimics insulin - and can even bind to insulin receptors. Because of this, elevated IGF-1 levels are associated with an increased risk of developing adult onset diabetes. 
As you can see, much of the chronic disease has its roots in an increased production and overstimulation of IGF-1. Verifying this is a significant body of research evidence that shows that lowering IGF-1 is one of the more significant anti-aging strategies. (You don't want to go too low with IGF-1 though!) Trying to summarize all the research in this area would be a huge task, but let me give you some teaser facts on the subject:
a) Caloric Restriction is the only legitimate life-extending strategy to date. Researchers have estimated that approximately half of its benefit comes from lowered IGF-1 levels. 
b) Lower IGF-1 levels are associated with decreased risk for developing prediabetes, diabetes and many types of cancer as mentioned above. Look at what one study author wrote about the cancer connection for example:
"While this may appear disadvantageous to vegans, a correlation is hypothesized between protein quality, insulin-like growth factor 1 (IGF-1) and increased incidence in prostate and breast cancer. IGF-1 (a somatomedin hormone) has a well-documented role in stimulation of prolific neoplastic cell growth. One study reviewing correlations between varying cancers and IGF-1 found consistently high RR [Relative Risk] ascribed to colorectal cancer, premenopausal breast cancer and late stage colorectal cancer." 
c) Lower IGF-1 levels actually switch on repair genes that are responsible for powerful life-preserving and extending effects. This appears to be one of the keys to Intermittent Fasting, which many of you have undoubtedly read about. 
2. Cancer Protection. If plant proteins and plant-based eating in general really protects against cancer, then one would expect vegans to have the best cancer rates. The reason I say that is that vegetarians generally eat a lot of plants but they also consume a lot of animal protein as well in the form of dairy and/or eggs. Both eggs and dairy can stimulate IGF-1 particularly well. Only vegans uniquely consume both a lot of plants and exclusively plant proteins. Is there any evidence that veganism actually protects against cancer?
a) A vegan diet, due to its generally lower methionine content, has been shown, as expected, to lower IGF-1 levels. 
b) There are only 3 studies that I know of that have look veganism and compared them to meat eaters, vegetarians or the general population. The results seem compelling in my opinion:
--Vegans had a 19% lower overall cancer rate than the general population in the EPIC Oxford Study and significantly lower than vegetarians as well. 
--Vegans had a 15% lower overall cancer rate than the general population in both Adventist Health Studies and significantly lower than vegetarians as well. 
Now if you eat too much of any protein, it will likely raise IGF-1, so keep that in mind. I take some supplemental plant protein for muscle building and so this likely raises my IGF-1 a little, but not nearly as much as if I was consuming exclusively animal protein.
3. Unstoppable Gains. Many guys coming to this site are interested in gaining muscle for health, athletic and/or bedroom purposes. What's the only thing that can stop them from gaining muscle, assuming they have a decent diet, workout plan and hormone levels? Things like cancer - Metabolic Syndrome - diabetes. That's right - these chronic diseases are what will take them out of the gym and into the doc's office or emergency room. Of course, plant proteins and a plant-based diet in general can give you the best odds possible in my opinion to keep you exercising and building muscle year after year and decade after decade.
NOTE: You may also need to reverse arterial plaque. Well, the following two Plaque Reversers as I call them, are either entirely or largely plant-based. See my reviews of Heal Your Heart by Dr. Gould and Prevent and Reverse Heart Disease by Dr. Esselstyn for examples.
If you stop and think about it, it you put on just 1 pound of muscle for a decade, that's 120 pounds of muscle! Well, that's not too likely to happen obviously, but my point is that the steady accumulation of muscle can lead to a massive physique over the years and you don't have to risk life and limb.
I am 54, working lots of extra hours per week with 3 kids and a day job - you know the story since yours is probably similar - and I have put on muscle steadily since going to plant based proteins. (I do consume a BPA-free can of sardines almost every day, so I'm not completely vegan.)
The way that I do it is that I take four supplemental proteins every day: a) BPA-free sardines, b) excitotoxin-free rice protein, c) excitotoxin-free hemp protein and d) nutritional yeast. I get about 25 grams of protein from each, so that is about 100 grams of protein every day. In addition, I get about 40 grams of protein from other plant-based sources, bringing my total up to about 140 grams/day. (About 82% of my protein is plant and 18% animal.)
Now I currently weigh 75 kg (165 lb), so that is 1.87 g/kg. Some of you fellow gym rats may be thinking that a) I am not consuming enough protein, i.e. a gram per pound and b) I am being foolish because my protein quality is low. Let me address each of those:
a) The 1 gram per pound is a complete myth. The actual NASM guidlelines are 1.2-1.7 g/kg for strength and weigh training. Clearly I am well above that.
b) While it is true that my protein quality is singificantly lower, it is probably only about 25% lower. If we multiply .75*1.87 g/kg, we would still get 1.40 g/kg which is right in the middle of the above range. Again, I have found this to be plenty of protein for muscle gains and I realized that I had been consuming WAY too much protein over the years.
4. HRT Protection. I had a high PSA read and the HRT clinic I was going at the time immediately dropped me took me off of testosterone. You can read my story on my page High PSA But No Cancer. Of course, the concern was the possibility of prostate cancer. It turns out that almost for sure I did not have prostate cancer, but it was a sobering experience for me. I realized just how fragile my HRT really was and that I had to focus on cancer as well. Being a family man, I knew what I had to do and went on plant proteins immediately as I described above. (I have seen added the BPA-free sardines for the extra omega-3's.)
5. Incresaed Energy, Endurance and Alertness. This is one benefit of plant-based eating and plant-based proteins that I cannot prove but have personally experienced. Anecdotally, many people on vegan diets - or those who are darn close like myself - love the increased energy that they experince. Look at whatTony Gonzalez, the NFL player who went vegan for awhile, wrote:
"Now he talks about how much faster he recovers from game day, and how his energy has sky-rocketed. "It's unbelievable how good I feel," Gonzalez said. "Seriously, my recovery is so much better than it's ever been, and my endurance is tremendous. The best part is that during games I really don't get tired. I have more focus, too. I'm even staying awake in meetings." 
He did eventually go off of veganism, because he wanted maximum muscle growth. Since I am not in the NFL, I love it and enjoy putting on muscle AND a nice boost in energy.
3) Bioscience Horizons, 2010, 3(2):197-212, "A scientific review of the reported effects of vegan nutrition on the occurrence and prevalence of cancer and cardiovascular disease"
6) Cancer Epidemiol Biomarkers Prev, 2013 Feb, 22(2):286-94, "Vegetarian diets and the incidence of cancer in a low-risk population"
7) Eur J Endocrinol, 2011 Feb, 164(2):223-9, "Prediction of incident diabetes mellitus by baseline IGF1 levels"