Invert this rule to get the maximum age you can date (defined as the person whose minimum age is your current age):
min age = (your age / 2) + 7 max age = (your age * 2) - 14
If you're 30, then you can reasonably date people between 22 and 46. So the other guy can add even more years before 1990.
I don't know if I trust your answer based on your username