Try team sports. Playing the sport is exercise that's fun, but also your team practice sessions are largely exercise as well. You're doing it alongside your buddies so there's lots of joking around and whatnot so its fun.

What's more is it makes the practical effects more immediate. Delayed gratification is hard. Results that are going to be realised soon are much more motivating.

So when you're doing something like running by yourself, it's still easier because you're not running out of some vague sense of being more attractive in a year, or avoiding a heart attack that you may or may not have in 10, you're running so that next weekend it's ever so harder for the opposing teams front rowers to flatten you.