Is 17 yrs too late to start professional athletics?

Hi. This question is more for a friend than me. He is in my opinion a very good runner, sprinter i mean.His time for 100m is 10:50-11.00secs. which i thought was quite good, and just in a talk i asked him why doesn't he take up pro athletics. I guessed that with practice and all, he could have reduced his time to 10 secs which is quite good in a competition or even 9.00-10.00secs which is even better and more suitable for bigger tournaments. But then i thought that maybe it is too late. I was told that people who want to go for pro athletics practice it at an earlier age so that their blood vessels thicken, and the blood supply increases ++ stamina, lung capacity etc. Like pro pianists, sportsmen, footballers don't they have to start from an earlier age?