Here’s the thing: the younger the human is, the more crinch this becomes. I have personally no problem with a 30-year-old and 130 year old getting together. But 18 and 118? Yikes.
Here’s why: once you enter the work force, life changes pretty rapidly and the way you view the world changes. The difference in lifestyle between a teenager and an adult is so vast that I find it impossible to imagine an intellectual and emotional romance between those two age groups. What would they even talk about? But once you’ve been living on your own for a while, have some working experience, the age differences between two adults, even by decades, doesn’t matter as much.
What about immortals that look like teenagers? you may ask. As someone pushing thirty who is constantly told I look like I’m fourteen, I can tell you, I would never pretend to be a teenager, even if I look it. Being an adult is infinitely better and, again, it is just a completely different mindset to be a working adult vs. in-school young adult. Tons of people look younger than they are and this is no excuse for going through high school over and over again. Also, not an excuse for falling in love with someone who has never filed taxes or who thinks a hundred bucks is a lot of money.
Make them both adults (and I’m not talking barely legal, I just graduated high school adults) and I don’t think the age difference even matters.