I’m 60 and can relate to weird hand problems a we age.
Very hard to tell with this…pain could be coming from the fingertip as well and radiating up the finger (I’ve had this happen from pressing too hard)…
You can experiment with different .hand positions to see if it helps, but I’d recommend a hand dr. look at it, to see if there are other problems, if it doesn’t get better soon.
Do you use a strap? It might help to put less pressure on that knuckle…
Not having feeling isn’t a good sign…could have to do with circulation or nerves…best to get a professional opinion I believe.
Dave