I'm 36, so I can't speak from experience like you can, but the main things are to just do what you can, don't over do it and just be sensible and if you sometimes need a little more rest during sessions than younger people might, take the rest and also just work at your own pace, don't be tempted to over-exert, or do more with the mind that the body cannot do.
People say about many things that it's 20% physical and 80% mental, but the body cannot willingly obey, everything the mind wills it to do, because it has limits.
You will, if you haven't already, find some or all of those limits and it will allow you to work to a level that is tolerable and will not induce elevated physical risk, in relation to one or more things.
So keep pushing, keep believing in yourself, but just use a modicum of common sense
Oh and be proud of yourself, for not giving up on yourself and thinking you're too old to do much good with your carcass now, because you're not and people can still achieve quite a lot of physical good, even when they're over 50 and basically starting from scratch