Your age, divided by 2, then add 7 = minimum age that most of society will deem okay.
For example:
25 ÷ 2 = 12.5 + 7 = 19.5
So the acceptable age for you to date that avoids the 'ick' is around 19 years old. Honestly it's not a big deal in the long run.
For me as long as your above 18 and it's consentual (ie. not forced, pressured, or groomed, etc), it's fine.
This is the only semi-legitimate reason I can get behind. For kids in grade-school.
If anybody outside of grade-school brings this up, I would laugh and ignore.