^ This is a sensible idea.
The age of consent for characters across the board remains at 18, but romantic relations could be limited to a 2x age difference for all races. So, a 20 yo human max partner is 40, 40 with 80, etc -- a 100 yo Elf max partner is 200, etc. Once a character is 300, 400... it doesn't seem like it really matters if they're romantically involved with someone who is 600 or 800, which are increasingly rare ages anyway.
Yeah it's going to restrict 80 yo's from dating 20 yo's and 500 yo's from dating 100 yo's, but are there seriously that many relationships with ages that are so far apart? I'd be genuinely surprised if so. A character who has been around since 1, 2, 3.0 probably just shouldn't be romantically involved with a character born in a recent map. Seems to me like it would be culturally inappropriate for an ancient Elf or Dwarf to procreate with someone who could potentially be a descendant of theirs (whether by blood or not).
Edit: Alternatively -if we think the 2x rule would allow for too big of an age gap- then we just set an acceptable age gap between each race that seems culturally appropriate. I.e., 20 years for humans, 50 years for Dwarves, and 100 years for elves...