No, most everyone with any sense slows way down on the ukemi [falling practice]after about 40 or 45 and stops almost entirely sometime soon after that. This is simple self-protection. Fortunately, you don't have to fall down to do aikido...
I have run a decent-sized cohort of beginners [in their 80's] and they did great...
These octogenerians did aikido just like everyone else and worked on the same stuff.
The only other training tool common in aikido that I'd dispense with for 80 year olds is suwari [practicing techniques while kneeling] - but that is an after-black-belt thing anyway. sort of a neat little bit of historical preservation, and not really a core training method of aikido. I have seen people with bad knees perform suwari seated in chairs. Works great. So, in summary, yes, 80 year olds can do all the same aikido that the youngsters do - except ukemi and kneeling suwariwaza.
- No suwariwaza (kneeling techniques), or perhaps suwari from chair
- Minimal, easy ukemi (falling), maybe only w/ crashpad
- Emphasis on lower extremity strength/flexibility and balance. Footwork exercises can be done very slowly, leading to great increases in balance and mobility. Basically this is aikido done in a slow, deliberate way in order to get some of the proven benefits of taichi. Note that I'm not saying that slow aiki=taichi. It is not, but slow aiki does have some of the same physical health benefits as slow taichi practice.
- Wrist releases and chains of techniques based on wrist releases
- Evasion and brush-off
- Toshu randori (slow sparring) again, I am hesitant to draw connections between aikido and taichi, but this slow-motion partner exercise has many similarities to some of the push-hands practice I've seen tai chi guys doing.
Working in this way on this large subset of aikido is easily within many elders' ability and it produces great martial artists, in many ways equal or superior to their younger counterparts.