It's not just the body that's 52, it's also the mind.
I don't think I absorb new ideas as fast now as I used to. Grappling is very conceptual, in a way, there are so many things to learn, and you then have to think of applying them. I find that even though I have learned a new technique, I need to be reminded while grappling to use it--"he's letting you have his right arm, go for the choke." It's hard to see the tactical opportunities sometimes, especially in grappling.
On the other hand, I do think I often see the bigger picture more clearly now than when I was young and, say, playing basketball (I wasn't a martial arts student until I was 44, basically). For instance, in sparring: "Frank has a great left hook, so I should do the unusual and circle towards his right, even though he's right-handed."
My pulled groin muscle is improving, I can walk upstairs at a normal pace. I'm skipping grappling class tonight because I'm going out of town, but that's just as well, I need a bit more healing.