Elderly reptiles? What do you do?

So I've never had this issue before in my reptile collection. I've dealt with it in my dogs, and horses. However, I'm dealing with this question in two of my favorites. I have a 21 year old rat snake who's no longer a spring chicken, and a 18 year old blue tongue who has very much so slowed down.

My ratsnake is a wonderful old gentleman. He's gone downhill in terms of eating. When a few years ago he ate XL rats every week without fail, he now manages only a medium rat at most twice a month. Many months, he will refuse and only consume one medium once that month. He also enjoys higher temps and more basking. He's been such a great companion! I wonder if there's anything I can do to make his last years more comfortable?

My blue tongue is a doll, but looking through pics the other day I've noticed how much she's changed. From the fact that she no longer hunts food (no cricket chasing here!) to her preferring chopped up little pieces of food now vs her mowing down good sized pieces in the past. She rarely climbs anymore. She still gets excited for a raspberry, but she'd rather just open her mouth for you to plop it in.

Do they have geriatric guidelines for aging reptiles? At what point do you consider the inevitable for an elderly reptile?

I've had to put down very few reptiles due solely to old age. Usually some ailment or affliction resulting from the older age takes the decision away for me. For me, I look at the life expectancy of that specific animal and just really evaluate it's life. If it's keeping weight and not in pain, I don't get as concerned if it's not moving as much or not climbing. If it's losing weight, reacting to or is in pain, or having a reoccurring, dangerous health issue...that's usually when I make the call. For their enclosures, I usually make sure to lower any of the climbs and provide a bit more bedding.