No its not too late,you can still fight at a high level if you are prepared to put in the hard work. I know people who have taken it up in their 30s and still can compete at a decent level.
Sergio Martinez studied boxing at that age,why not you?
Bit late--Still you may proceed.
I have always wanted to box and until recently I haven't been able to, But now I can and I'm loving it. I go to boxing twice a week, run 6 days a week and do core exercises 3 times a week. I have to able to do fights etc and try to go as far as I can, Do you think 20 is too old to start boxing and to go to a high level?