Yes but, like Olympic gymnasts, you’re going to have to give up on the concept of them having a social life. They’ll also be well outside the range of what most “normal” teens can relate to. It’s a very specific lifestyle choice that will chew up the entirety of their life until they’re done.
Olympic level training is all day, every day. You eat, sleep, and breathe it.
A realistic version of the “ridiculously skilled teen” trope basically requires sacrificing everything that is not directly related to the skills they are acquiring. A lot of kids when in training for the Olympics are home schooled or taught by a tutor in the off hours. They don’t go to public school.
Most of the time, in fiction, when you’re looking at the ‘ridiculously skilled teen’ the author doesn’t pay their dues. They don’t take into account the sacrifices made by these children, their parents, and their instructors to reach this pinnacle of excellence. They look at the intensity of the hard work involved and often assume that it was forced. That the child was actively denied life experiences by the evil adults in their lives. That they’ll turn around and change their tune if they just have a chance to experience real life, friends, or normal experiences like the ones the author had.
Their ridiculously skilled teen got where they are because they were the winner of the genetic lottery and in possession of great talent.
They don’t take into account the defining factor of the champion: personal drive.
The problem with this approach is that talent is only one part of the equation. You can have a child who is so talented as to make the angels weep in joy but if their talent is not backed up by a personal desire to excel then they are destined for the halls of mediocrity.
Even if you put a child through the training you suggested in your ask, a ridiculously skilled teen is not a guarantee. They’ll be more skilled than the average, and certainly better than one who never went through the training at all but they won’t be in the champion ranks.
To get a ridiculously skilled teen in real life, you need a mix of talent and drive. The child to choose their training. They love it so much they don’t suffer burn out. It’s what they want to do. They are the ones who push themselves and strive for it. Their authority figures are the ones aiding the child in their drive.
They. Have. To. Want. It.
You can have a kid who has been training for fourteen years who is simply mediocre. The amount of time involved is not a guarantee for excellence. It’s a gamble. Not just on proficiency, but on desire.
If the prodigy wants out, then the prodigy falls behind. To be the best is not a guarantee, it is the goal we strive for. It is a spot for which there is intense competition. They earn those skills and earn that spot. They fight for their training’s pace. And it can be very hard for people who’ve never been in the rat race to be the toughest, the smartest, the strongest, or the best to contemplate or understand.
These are kids who when given the choice between going to a birthday party or bowling with their friends and training chose training. All the sacrifices they make are sacrifices they chose to make. No one is forcing them to do anything. You can’t reach that level of excellence without that desire and drive, that willingness to make sacrifices, that choice.
Often, the “ridiculously skilled teen” trope is paired with “but they forced me to do it” trope.
You don’t get to be that good without intent and the desire to be that good.
Kids that want a normal life quit and, when they’ve quit in their minds, it’s over. An authority figure can force them to show up, can use whatever outside motivation they think will work, but if the kid doesn’t want it then they won’t do it. They’ll still be “good enough” and that’s most martial artists/soldiers. They may end up “slightly better than average” but they’re not going to be at the top of their game, much less the game itself.
This is the child who when given the option between more training and an hour of television, chose training.
This is the child who when given the option to socialize with friends, chose their training.
This is the child when given the chance to go on vacation, chose training.
This is the child who made the other children nervous because they were obsessive. Still doing their thing when their differences stopped being cool and the other kids ran off to play somewhere else.
They love it. They have goals. They want to be the best.
If you want to write children or teens who fit this mold, the best media for you to turn to are sports movies. This includes the really schlocky movies like Mighty Ducks or ones based on real life champions like Olympian Gabby Douglas. Basically, most of the cliche feel good pick me ups that are often scoffed at when we hit our teenage years. Situations change, but your ‘ridiculously skilled teen’ will have more in common with the characters of Center Stage than they will Buffy. And in a comparison of slayers, Kendra still fits this trope better.
So, with a character who is ridiculously skilled, you make sacrifices. They make sacrifices. And maybe they’ll hit the point where their body starts falling apart in their late twenties/early thirties where they start having regrets, but it won’t be in this moment.
The thing to remember when crafting these characters is that the level of skill they possess isn’t easy to reach. They aren’t actually any different from your average mortal except that they want to be this way.
This, whatever it is, is what they love to do. More than friends, more than relationships, more than love shared with other humans. This is who they are in their bones and in their soul.
To get a teen ridiculously skilled in martial combat, you need a character who is in love with the art of war.