I beg to differ on the physical conditioning. Treadmills are fine, but pushups and situps and whole body calisthenics, especially done in ladders, can be more beneficial. Very often, its the weakness in the core muscles as well as balance that make someone weak or strong. Focusing on these - core and balance - can compensate for weaknesses in other areas. I'd look up "Yoga for Regular Guys" and Pavel Tsatsouline. Both exercise regimes can be done at home with minimal equipment in 20-30 min per day. The latter develops explosive strength which is what is needed to feel confident about defending oneself.
I changed my weight training the last year and have increased my max by 50% in some areas. The easy gains come early, but it is the slow incrementals that add up over time. Diet, especially protein and milk intake, has a huge effect as well.
For a child who has not entered puberty, there is often no comparison to the man that emerges from the other side. Again, diet and exercise has huge affect as does the maturing of the immune system. Ugly duckling rule applies to boys as well.
