This happens in the episode where everyone prematurely ages, and they are sent through the transporter to make them their "normal" ages. There's no reason given why they couldn't do that all the time.
I assume there's some in universe reason why they can't / don't keep copies of the teleportation data, otherwise everyone would be effectively indestructible
"Oh no the captain got eaten by a space tiger"
"No problem, I'll teleport a backup from an hour ago, he'll be there in 5 minutes"
There are multiple answers, with different degrees of truth
The patterns aren't (typically) stored long term, something implied about transporter buffers seems to indicate they can hold incredible amounts of data that starts to degrade very quickly. New patterns are taken each time they transport AFAIK.
But, instead maybe that "cell damage" is just part of the details you get when you retain enough pattern detail to include peoples recent memories.
But, instead maybe the actors age in real life and keeping track of making them look perpetually youthful with makeup would be really hard so whatever the excuse is it's just an excuse.
If the meme is correct that people are rebuilt at the molecular level, then cell damage would be preserved across iterations.
That said, if you have sufficient resolution and detail to rebuild someone at the molecular level, I see no theoretical limitation that would prevent actively using modified transporters to heal damage, etc.
That said, I subscribe to the philosophy that your subjective experience / perspective / consciousness ends the moment you're first disassembled by a transporter and never resumes (i.e. transporters are actually duplicators). So it's not the fountain of youth in any meaningful sense if transporting is modified to repair damage.
That said, I see no reason why a heavily modified transporter couldn't be used to Ship of Theseus your whole self cell by cell, thereby completely rejuvenating yourcellf without the pesky cessation of consciousness / death. So, yes, it could be the fountain of youth.
What if you went in with an empty stomach and came back after a night of binging on shore leave, alcohol, unsafe sex with strange aliens, too many nacho plates filled with guac, salsa and sour cream and an unhealthy amount of sweets, chocolates and fried food ... you're beamed back to the ship with an empty stomach again and no diseases.
i mean it's effectively just cloning, which doesn't transfer any memories made after the last scan, since it.. isn't magic..
i think dark matter is the closest i've seen to a show that actually acknowledges that this is how that kind of tech would work, and it's a damn shame it was cancelled..
i imagine that in the trek universe the tech would be extremely regulated, probably only allowed to be used in situations where people are very likely to die and thus circumventing the death entirely. Now, with away missions that becomes more difficult as you can't strictly know when someone's actually dead, and i'd imagine the federation would look very dimly upon having two copies of people walking around..
Read an old Larry Niven story where he used this idea. Back in the 1900's scientists theorized that aging was caused by garbage building up in the cells. If you transported and left the garbage behind your body would revert to a younger stage without memory loss.
I don't accept the premise -- the pattern is read on transport, yes? Rather than a fixed record of one's composition. Therefore, the only aging you won't be doing is for the duration of the transport process itself. Chump change.
This sort of teleportation also effectively kills you, right? Once you are molecularly demolished, your direct stream of consciousness stops, while "you" who steps out of a teleportation machine in a destination point is your perfect copy with implanted memories.
You die every time you go into the transporter. The transporter has a heck of a time saving your consciousness/soul. A husk that resembles you and has your memories comes out the other side, but the moment you enter the transporter its nighty night.
Thomas Riker is younger than William Riker, so this is observed fact, not just crazy "Jesse" theorizing...except that we continue aging when not being transported, so we wouldn't stop aging unless the transporters were set up to keep a specifically aged body to materialize, but also have a current version of our brain. Sounds pretty complicated.