well, i'd say wait, but i did it my first time at 22.....didn't notice a lot from it as i only went 3 months
i guess it all depends on your goals.....if you are desiring to be a national competitor and make bodybuilding yoru life, i say go for it, if you are not going to compete at a high level i say wait.
i started on it again after my surgeries from my bike wreck for a few months, then back off, then back on again last december and am running it all year.....loving it right now, im 27