How would you fix your brain? Its capacity is obviously limited, and tinkering with plasticity almost certainly will have unexpected and undesirable consequences. You simply won't be the same person.
Is it obvious? How would you repair a piece of metal suffering metal fatigue? A perished elastic band? A screw with a chewed head? These are trivial things compared to a human body and we haven't a clue how to rejuvenate them, all we can do is replace them. But how do you replace "a muscle" without surgically damaging the tissue around it? How do you keep "muscle memory" after doing so? How do you reconnect your replacement eye to the optic nerve? How do you replace cells like for like when there's tens of trillions of them in each person, and each cell is a machine a hundred trillion atoms complex? How do you target the cellular machinary inside one cell and find out that it's in need of repair? Is it 'pretty obvious' you can do so?
What does it mean to reverse aging? Younger me was smaller. Younger me moved differently. Younger me liked different foods and knew different facts. Younger me didn't have scar tissue in certain places, are you going to swap that out for normal tissue (how)?
It's pretty obvious that 'repair' does not undo the effects of ageing, it prolongs them - restored old cars are not new cars, they still need to be driven gently. People with plastic surgery don't look like young people, they look like old people who fell into uncanny valley.
The huge difference between repairing a piece of metal, and repairing a living tissue, is, obviously, the living tissue can repair itself. The mechanisms of self-repair are built in, and they are extremely effective. The problem is these mechanisms break down with age, so the task becomes figuring out how to re-enable them. Yes, we don't know how to do that yet, but keep in mind - just 10 years ago we didn't know how to do things like CRISPR gene editing and now we can do something like this: https://www.bbc.com/news/health-63859184. The point is, we are making progress towards the goal of controlling all the processes in our bodies. There's absolutely no reason to believe this progress will stop any time soon. Even if we can't do it today, things like organ or limb regeneration do not sound like science fiction any more, it's a question of when, not if.
Yes, it's quite likely every one of us Millennials will grow old and die, but I'm much less sure about our kids, and our grand kids will most likely be able to stay forever young if they so desire.