Is it weird to date someone 7 years older?

No. There is this rule of thumb that says: half the age of the older partner plus seven is the socially acceptable minimum age. You are both of age. So, no problem.

Is 6 years age gap bad?

6 years is just fine as long as the younger one is +18. I have a 7 years gap with my girlfriend and there havent been any problems, at all. If youre the older one, you just really have to remember what and how you felt at that age.