let me rant for a minute about how fucked up it is that "fitness" gets pushed first on teenagers as 1) school sports/athletics (which cause a statistically enormous amount of lifelong injuries) and then as 2) instagram gym culture aka being skinny+muscular for aesthetics. we pretend this is what "health" looks like, and it's not.
fitness & excercise should be about improving your day-to-day life. which means fitness needs vary a lot by individual, age, medical conditions etc. here are just a few examples of what practical fitness goals can look like:
stretches/exercises to reduce pain in daily life (e.g. carrying groceries up a flight of stairs without being sore the next day)
increase mobility (e.g. walking around a museum with fewer rest periods)
increase stamina (e.g. running to catch a bus)
increase muscle mass e.g. to prepare for your 60s/70s, bc apparently that stuff sticks around and makes getting older waaaaay easier
increase balance/flexibility to prevent falls
general injury prevention, bc that shit sucks
basic maintenance, to help preserve a lifestyle that works for you
screw this anti-aging bullshit. no one needs to be a professional athlete or permenantly 21. what we deserve is to be able to age comfortably and live long, fulfilling lives. fitness is a tool, not a moral duty. it should work for you, not vice versa.