Tons of people reach Butch Wonders by searching for things like "lesbian age differences," "age difference formula gay," and "what's the rule for gay age differences?" I can yammer on for days about how it's silly to have a "formula," how all relationships are unique, and yada yada yada. But at the end of the day, people want an easy answer.
So here's your easy answer. In the gay community, we get a bit more leeway. The acceptable age difference for us is wider than it is for straight people, and the difference grows as we age.
The age difference formula for same-sex relationships is graphed below. We are in blue; opposite-sex relationships are in red. (I know this doesn't take into account bi-gendered people and many other shades of queer, but that involved parabolas and was just too complicated.) The formula is one-third your age plus ten years.
This took extremely difficult, comprehensive, and painstaking research on my part--not to mention, many sleepless nights. Now let's practice.
If you're straight and 30, you can date a 22-year-old. If you're gay and 30, a 20-year-old. 48 and straight? A 31-year-old. But 48 and gay? a 26-year-old. Ka-bam! You've got it!
So, now you know. There's your formula. One-third your age plus 10. If you deviate from it simply to make yourself "happy," or because you've "fallen in love" or whatever, know that you're contravening science itself.