Players are quite different, some peak early, and some peak quite late. there are so many variables in the equation. Drogba wasn't a big name in football until the season he moved to Chelsea or the season before that, and he wan't that young when he moved. yet, at 33, he still is a great player.
Both Owen and Fowler could not achieve much because of their injuries. also, they're quite different than Carroll. he's not all about pace and skill, he's a big strong goal poacher. he peaks with experience more than anything.
one last thing, if Carroll wasn't THE striker we are looking for, we can always buy another striker.