Down here in the south west it's a retirement area and as a result we have a significantly higher proportion of older shooters than other regions. In my own club we have several with mobility issues, our treasurer walks with a stick and our child protection officer has almost no use of his knees. They both take part in as many activities as possible and we certainly don't stand and watch them suffer; we alter what we do so as to be as inclusive as possible.
In the south west region we shoot our own version of HFT which does allow sitting, it does allow scope adjustment to give a clear sight picture, and these may be seen as "concessions" to age and frailty. But it also pushes distances out to 55 yards which sorts the old men from the older men...!
We don't have any enforced prone targets. We have plenty that you can take prone if you wish and are able, but there is always an alternative position even though it might be very tricky.
I shall be 68 in a few days time, and whilst I am fortunately reasonably capable of the usual movements, frankly I'll leave close contact between belly and grass to those who revel in it, I don't. I choose to take almost all HFT shots from a kneeling position, firstly because I can, and secondly it makes a change from sitting.
I'll just add that our scope rule says, (paraphrased), rangefind with the naked eye, set your focus accordingly before you look through the scope at that target. If you have raised the scope to your eye, you have to live with whatever the settings are, for that target. Maximum 12x mag, no dialling clicks, just holdover.