18? I'm betting the whole events of bleach have probably taken place in one year. 16 at most
Again, I don't think it's weird since she isn't a kid. I don't remember how old he is, but it's not like a 10 year difference is uncommon if that's the case. Hell, my dad was 32 when he married my 22 year old mom for example. Whatever floats your boat though, but I still recommend it.