Like with any supplements it is important to select the best quality product possible. Something with the right ingredients, produced to high standards and a proven track record of achieving results. There are lots of test boosters on the market so it can be hard to decide on which one to pick, trust me I have been through them all. Over YEARS of experimenting with different brands, ingredients and formulas I can safely say that TestoGen has been my favourite testosterone booster . Why? Because it is the only brand that I have found to consistently deliver noticeable results again and again with not only myself but all of my clients. No hype, just results .
Testosterone is significantly correlated with aggression and competitive behaviour and is directly facilitated by the latter. There are two theories on the role of testosterone in aggression and competition.  The first one is the challenge hypothesis which states that testosterone would increase during puberty thus facilitating reproductive and competitive behaviour which would include aggression.  Thus it is the challenge of competition among males of the species that facilitates aggression and violence.  Studies conducted have found direct correlation between testosterone and dominance especially among the most violent criminals in prison who had the highest testosterone levels.  The same research also found fathers (those outside competitive environments) had the lowest testosterone levels compared to other males. 
Starting from the age of 30, your testosterone levels (T levels) begin to decline. Stress, lifestyle and environmental toxins will further diminish your testosterone production. Research has shown that it drops by 1 to 2 percent a year after age 40. At that gradual rate, most men don't notice the decline until they hit their 50s, when symptoms such as reduced energy, weight gain, depression, poor health, muscle loss, brittle bones and loss of libido start to appear. By the time you're 80, more than half your testosterone could be gone.