I am 68 and my penis is just a bit on the long side so it needs more blood flow to get a good erection. Even at peak times, my penis is a little floppy but works okay for oral sex.
On the other hand, I find it very difficult to penetrate an anus without a pill. The pills can be hit or miss; usually they help a little but not a lot. Sometimes I still cannot penetrate even after a pill.
I also learned that if I hope to penetrate an anus, I cannot spend too much time in foreplay. My penis is hardest when I first drop my trousers. The longer I wait to penetrate, the more risk I take that my erection will get too spongey to enter.
My last experience was about two months ago, I penetrated a man's anus but could not get the in and out action going. Instead, every time I pushed in, my penis kept bending instead of going deeper.
I imagine my penis would be able to penetrate a vagina, but I have not had that opportunity in years. I can only seem to connect with guys.
By the way, my boyfriend is 69 and has no problem at all with his erection. I think I might be able to hang a towel on his stiffie.