Both Good friend and I turned 40 the same year. Hers was a few months before mine. We ended up going for a very expensive meal for hers and I spent a fair bit on her present. I made quite a fuss of her. I even made her a cake.
Then it was mine. She was on holiday when I celebrated it but she told me she had a gift for me and we’d celebrate some other time. I’ve seen her a good number of times since then and it has never materialised. That’s absolutely fine, I’m not a child, but she annoyingly keeps bringing it up e.g. “oh, I must bring your present”. She doesn’t live far so it’s not hard to drop it off.
AIBU to say the moment has passed and stop bringing it up. The main reason being that last month was my 41st and the moment really has passed. I don’t want to be still having this conversation when I am 60. I am a bit miffed that hers was a massive event but mine was unimportant but that’s fine, I’ve learned my lesson.