Just talking about released games I’ve played:
In Community College Hero, you play a young adult (I think about 18 to 21 years old probably?) and one of the ROs, Crook, is about 30 years old.
The Mysteries of Baroque has an RO who I think is in at least his 40s, probably 50s as he has an adult son. The MC is probably in their 20s to 30s, I’d guess.
The Evertree series hasn’t quite reached that stage yet, but it was hinted at the end of the second game - Sordwin: The Evertree Saga - that one of the possible allies from the first game - Evertree Inn - could become an RO in the next installment. He’s a mature 38 years old half-orc. There’s also a female dwarven RO you can have in the second game who is 41 years old. Though if these characters can be considered older than you does depend on the race you choose for MC. An elven MC e.g. is stated to be 37 years old in book 2, while a halfling MC is 18 years old.
There are a bunch of games where the MC and the ROs are both mature, so that probably doesn’t count into what you mean with “older love interests”, maybe only from the player’s perspective when the player is younger than MC. Games like that are e.g. Rent-a-Vice, A Study in Steampunk, or Fallen Hero (MC is in their early 30s, at least two ROs are in their 40s, and one male RO is actually in their early 20s, so younger than MC).
Others have mentioned Tin Star - two male ROs are older than MC, and I think Dan Schmidt is the oldest of the ROs in that game? At least he has a lot of stories to share.