Well I think YES! ALL animals benefit from proper training as a youngster.
I personally don't "believe in" the practice of "imprinting"... and I do think some overhandling as youngsters makes for a pushier, more spoiled animal in the long run.
Most animals have a basic personality, and that you cannot change.
However, BAD HABITS are much quickly learned and a lot harder to break... so an older animal is more likely to have already created bad habits that you didn't have control over, and it will be harder for you to break and frustrating to the animal.
I feel that raising and handling a horse properly from the start (regadless if it's a MARE, GELDING OR STALLION) is important.
Andrea
Edited to add:
I sort of interpret from your post you are referring to neglecting to handle a colt while it is young, and letting it just be "wild" for a while and then hoping it's not hard to "train" it as a mature stallion?
Just remember, with domesticated animals that you want to "do something with" or "train to do something" it is going to be easier when it's an impressionable baby. The baby can learn your language easier than a mature horse trying to figure out your language. Isn't it easier if a foal learns that in our world, you get clipped, bathed, trailered, led, whatever and that's a routine part of life... rather than introducing uncomfortable and potentially scary things to a mature horse that hasn't had to deal with it. Most animals (including humans!) are basically lazy and would prefer not to work or pay attention. Soooo if the animal (or human!) has been allowed to be lazy and not pay attention for most of it's life or childhood, it's going to be a rough transition I'd think.
I dunno, that's my philosophy on it at any rate....