"Take care of your body in your 20s" It's easier to build muscle mass before the age of 30 and the muscle you gain during that time will never go away (with a minimum of training). The earlier you start exercising, the less difficult it will be to maintain your body as you get older. Someone who has never exercised but wants to lose weight by their 40s will have a much harder time than someone who started exercising…
Granting here, I'm sure it's definitely easier to resume old habits after injury recovery than to start completely fresh, so yeah, still start young if you're young. But if you're not, it's never too late until you're in the ground.