BJJ is great when you get older. I love judo and wrestling, but takedowns and throws (actually, just the part where you're on the receiving end
) gets harder as you get older. I can roll for an hour and come out of it feeling exhausted but great. Fifteen minutes of randori in judo as often as not leaves me wondering if I'm going to need a body cast at work the next day
The problem isn't strength (strength doesn't really fall off for most people until they hit 60 - the first guy to squat 1000 pounds did it in his late 40's), though speed, flexibility and agility fall off faster. And top level BJJ'ers like Jacare and Roger Gracie are as athletic as top level judoka or wrestlers.
The problem is recovery time ... it takes much longer for your body repair itself as you get older. Judo and wrestling are also very technical in nature, which is why you can't just go to the gym, get the strongest, most athletic guy in it and have an olympic caliber wrestler or judoka. But being thrown wears down the body, and as you get older it wears you down faster than your body heals.