Did he grow up?

I’m seriously not trying to throw shade so give me a break today. I just don’t see what my ex’s gf sees in him. He’s immature and she’s old enough to be his mother. They’ve been together 6 years. I told him 6 years ago that I bet she’d get tired of him and his childish jokes but nope, they’re still together. Did he suddenly get mature for her or what?