GD. said:
As others say, your body remains the same all your lives (unless you do a significant change in the structure of your soul first) so it will still be you, even if you die, just that you won't remember much of what happend before when you reincarnate.
But to point something out, don't ever think about that, you are here, you are alive, and you have the chance to change something and stop this cycle of reincarnation, do something about it, and instead of focusing on the fact that you don't want to die or that you'd rather die young than old, change your perspective and think about Life. Don't fear death but love life, this is what I'm trying to say here.
Aging without getting "old" is possible by keeping the telomerase levels as high as you can, which also makes you live longer, and this is done by an extremely healthy lifestyle and consistent meditation and training of the body, mind and soul in order to keep everything perfectly balanced.
Paimon showed me a few years ago how the telomers and telomerase levels have to do with aging and being immortal and how Magnum Opus changes every cell in one's body. Scientists have made pills which rise the levels of telomerase, and tested them on old people, seeing positive results which consisted in more energetic individuals, significantly reduced wrinkles on their skin and many more. I checked again now, as I've read that years ago, and now I see they even sell such pills and other similar supliments on amazon, I'm not sure if they did back then.
However, keep in mind that you should keep the levels high by meditating and being balanced in all areas of existence, which those individuals didn't do. It should be done naturally and you have the chance to start early. So basically you can prevent all the health problems which come with "aging" by doing all this stuff JoS provides us for free, and eventually do the Magnum Opus in the end, our primordial goal.