Good points, Eric, and I agree with you that as we progress in our Aikido our ukemi waza improves, but as we progress in age our physical ability degrades overall and all around. Bones become brittle, joints cease to function well, reconstructive surgery, bursitis, sciatica all can work to impede our range of motion and suppleness. Time waits for no man, and death comes to claim us all in the end...
Now at 40, maybe we can still take the high, hard falls and we even don't seem to land very hard, but how many 60-70 year olds do you know that are still willing to risk injury during aikido practice?
And, I'm not talking about ones ability to apply kaeshiwaza which in and of itself requires great ukemi skills, but in the course of regular aikido practice, on any given Sunday, the ukemi ability or willingness to participate 100% in a high fall or even overly aggressive ukemi diminishes.
I have seen a 70 yr old uchi-deshi in Japan, which is very motivating and inspiring, but he wasn't doing the hard ukemi either. Nor was anyone really willing to throw the guy hard.
Bottom line, even though I'm an optimist, as we get older our physical abilities in general decline, that is a fact of life, and if we include ukemi waza as part of our "physical aikido abilities" then, surely, we must face the reality that even though we may dream otherwise, there will be a decline.