RAAAAGE!!!! I just made a long-er post and the damn thing glitched out! I go to the Dark Side! But first, the question...
As far as I know clones life can be up to two times shorter than regular humans. Aging process might slow down when they are in their prime, but once they start getting old, aging goes back to fast, or can even become faster than before because of factors like stress. It was Kaminoans way to make clones, there were other. This way was just fine for Sidious' plan, and if not for Kaminos cloners uprising, he'd be making new generations.
Clones kept serving as Stromtroopers after CW, while younger ones were trained to become them until all was shut. As for new recruits, clones were very displeased with them. Clone CC-2224, older CW veteran, would call new troopers idiots who embarrass once remarkable military force.
For me OT the non-clone Stormtroopers are like Separatists Battle Droids: not very efficient, but are dangerous because of large numbers.