Age gaps have never bothered me personally; my dad is 10 years on my mum. My step dad growing up had 30 years on my mum (his youngest son is older than my mum; they split up) and my first relationship, he had 22 years on me. I also currently RP a character who has almost 20 years on his male partner - they're 30 and 50. And a girl who is 20 to her partner's 30.
Ages are just numbers, and while there are some restrictions (underage, most notably) all they really indicate is a base line of maturity and life experience. Some people experience a lot in a short period of time, and are able to better relate to an older partner, or even subconsciously seek out the security they are better able to offer. Some people mature faster or slower, and so relate better to someone in a different age range.
Like many others have said, so long as the pair are both consenting adults abiding by their local laws, then what they do and whom they are involved with should be their own business.