not being put into an old folk's home at 70 because you can't get out of a chair anymore
everyday tasks are easier and less sore
increased amounts of energy (working out should give you energy, not sap from it. if you're losing energy you're doing it wrong)
better mental health
you are more physically impressive to others
self esteem
being able to do any recreational or sports activity without effort or feeling like you have to miss out because you're unfit
the simple joy in just being able to move around freely without restriction or pain
The sense of achievement and satisfaction that only comes with working hard at something over a long period of time and accruing hard earned gains from it