Yeah, it could definitely be true. He was an ass at the bare minimum. It's hard to say, though. The MC never knew him before he started spending time with Rachel, so there's literally no way to know whether the first few years might have been better. She doesn't act like she has no experience to me — just like she has been out of practice for a very long time. It is probably limited, however: I doubt she's ever been eaten out, done anal, or anything along those lines. The damn's busted loose now, though, so the floods (metaphorical and between her legs) flow freely.
Honestly, I never thought the milf tag was for Rachel. I think it's there because of Sasha, who definitely is old enough to qualify for that. I always thought Rachel was high 20s, but definitely not to the age of a MILF.