Mind or body? help please?

hi i wondered if you could help i need your opinion, i am a fitness trainer i believe that it mind and body that keeps you moving easier when you get older, my husband say's its just your mind, how it all started was my neighbour who is 84 had a fall a couple of weeks ago it got me thinking, she's quite active i said to my husband do you think if you keep moving and keep active from young to old dose he think you would fall less be less reliant on others i,e opening jars doing the garden, he said muscle strength has nothing to do with it, i believe different, i believe if you keep your muscles strong even if your 65 by lifting weights ok maybe light ones compared to if you were say 25 but had been weight training since you were say 30 and kept it up from 30 to 65 would it make you feel less aches and pains when you move than if you didn't do it from the age of 30, my belief is if i keep myself fit and healthy both mentally and physically from 30 the onset of your body deteriorating will happen latter than some one who didn't work out or look after them selves, ok i know old people get ailments that cannot be avoided but i believe keeping yourself strong may delay them, but i agree mentally you have to be strong and determined but i believe its the combination of the two, my husbands argued its just mentally its going to happen at the same age weather you keep your body fit or not, i don't mind getting old it happens to us all it just sort of turned into an argument ( but he had been drinking ) but it upset me as i don't mind getting old just my nan died sitting in a chair not being able to move, i felt i was doing no i believed i was doing the best for my body to live till my dying day moving and not to worry my children that i couldn't get out of my chair or couldn't get to the shops, he has now gone to bed, was i just being naive thinking if i keep myself in good shape il be a stronger older person? or will i end up week and frail no matter what i do, i just want to be independent and not rely on my children, im 39 fit and healthy but has it all been for nothing? please tell your thoughts with me is it only mentally that you have to be strong or can i make it so i will still be able to open my own jars? Thanks Mandy x