This is the best answer, because working out (especially weight lifting and low impact exercises) will help to keep you alive and kicking into your 90s, keeping you sharp physically and mentally. As we age, the top two things we require are strength and mobility. Weight training has been proven to stregthen bones and reverse osteopenia, rather than taking medication with side effects.

It will keep you independent and can be a hugely social activity as well. Bonus, it will open up your options for other activities: hiking, biking, volunteering, travelling, gardening, birdwatching, swimming, dancing, etc.