Most Helpful Guy
While abiding by the laws of the state, I feel the age gap can be up to 4 years before the relationship becomes questionable.
I feel after 4 years, groups of people begin sharing different generational factors; only being able to relate to things others from the same age range would relate to, etc.
Most Helpful Girl
Once people are above 25/30ish, I'd say it's fine for them to make whatever decisions they want about dating age. That said, even at that age I'd say anything more than 50% of their age is kinda skeezy. Below 25, I'd say 5-7ish years is reasonable, and under 18 more like 2-3 years max.