Are fit people dull? Yes, next question please.
Fit people are generally very dull and spend most of their free time staying fit and not eating nice things. You will probably live longer being fit. But the increase in your lifespan is unlikely to dramatically outweigh the amount of time you spend exercising. And you don't enjoy exercising; that's why you are unfit.
Discretionary time is like discretionary spending, it is the bit we enjoy and makes the rest worthwhile.
You spend eight hours a day sleeping and abluting, ten hours a day working and travelling, two hours a day on duty in the home and two hours faffing about; which leaves only two hours a day which are actually yours to enjoy. If you then spend one of those doing something you don't want to do like running in a gym you are halving your "real life". And no amount of being a scrawny old bloke dribbling soup for a few extra years is going to make up for that.