To get an idea of what it's like to be the older Martial Artist. (And to you forty something year olds...kids, I have excuses older than your young asses.)
First - put a thirty pound pack on your back. Leave it there, forever.
Then find big, clunky shoes, a half size too small, that you would never dream of working out in, and put them on.
Put on gi pants that either don't fit, you don't like, or give you a mild rash.
Take the inside of your gi top and sprinkle it with course, short dog hairs. Or burrs from an overgrown field.
Squirt lemon juice in your eyes (you'll live, no worries)
Make sure you have little to absolutely no sleep the night before.
Have your friend hit one or two of your muscles with a ball peen hammer a couple hours before going to the dojo.
Then surround yourself with small, yappy dogs....that you would never hit, because you're a gentleman and you like dogs. But you sure do want to.
That's kind of like being an older Martial Artist.