A lot centers around how you read the series to gauge the power of transporters. Bear in mind these are machines that A: Can accidentally leave a full copy of you behind (Riker) B: Can take your body and split it into "good" and "evil" halves, later recombining them (Kirk) C: Can combine two unrelated life forms together into one (Tuvix) and separate them later and the coup de grace for this discussion D: Can turn you into a childhood version of yourself that still has your full memories (Picard, Guinan, a few others)

So, canonically, the "beam yourself into a younger you" problem is all but solved. Yes, with various minor environmental pokes and prods, but meh, they've demonstrated the ability to replicate those when necessary, so hardly a stopper.

That last one is one of the most egregious examples of how weird it is that nobody ever follows up on anything that happens in Star Trek. Whoops! Figured out how to turn an old man into a ~14 year old with all his memories! Ha ha, life sure is weird, but otherwise uninteresting, right? Unimportant! Move on!