If you're happy to be an instructor in a small flying club/school (god knows why) then you're never too old.
If you want to finish as a longhaul airline captain in a legacy/major airline then you should already be a professional pilot in some capacity by age 30, otherwise you're probably too old.
Everything else is somewhere inbetween.
There are exceptions of course (if you have "connections" for example) but generally the older you start out the narrower the options become. Thats a fact of life i'm afraid, not just in aviation but in most lines of work.
My advice, dont start at all now unless you like gambling with a lot of your own time, effort and money. Only start if you have a guaranteed job to go to. The pilot market is flooded, and i dont see it changing anytime soon.
Last edited by Private jet; 17th Sep 2013 at 10:17.