some things can be done
Lifting heavy weights thru the use of the major muscles (power lifting) increases testosterone. Squats, dead lifts, bench. Many boxers wouldn't want to do this. I'm a heavyweight (and nowhere near pro) so I'm not as concerned as some seem to be about it. There is a plant-based supplement called tribulus (If I remember the spelling correctly) that may increase testosterone levels. For the most part, many guys don't take care of their bodies to the level they should, which results in problems. You need sufficient sleep (I love when I can get 8 hours of it), rest, some power lifts, a diet high in vegetables, fruit, and lean protein. These things will really help most guys.
I'm 42 this month and, therefore, my test levels should be dropping. I seem to be doing ok (at least, my wife would probably say so). I still can pack on muscle (a sign that my hormone levels are not too bad) mainly because I try to do the things mentioned above. I don't do the tribulus. I also take vitamins C and B-complex every morning, along with policosanol (something a doctor suggested to lower cholesterol, and it really has helped me).
I hope this helps. I think you younger guys in your teens and early 20s really can take advantage as your normal levels should be good, as long as you take care of your health.