I started when I was 12. Coaches said it was a great time to begin, because your body is beginning to develop and the skills learned early will marry nice with the growth. In Canada you cannot fight until you are 12...so 11 seems a perfect age for here. The age limitations do vary by country.

Agree with everything Herb said regarding yourself. AIBA sanctioning for fighting cut off is 34. After that it is master class. But lots get into the sport of all ages for the conditioning, confidence, social outlet...lots of reasons. We have a few 60 yr old women in our gym who come for cardio, and do mitts once in a while.