A 13-year old and an 18-year old? Absolutely. A 23-year old and a 28-year old? No, though interests may be different due to where you are in life. A 20-year old and an 80-year old? I'm sorry, but in my opinion, that's nasty. I cannot help but think that there is some ulterior motive if the age difference is that great... but hey, it's happened before and sometimes, it actually is because they provide great companionship. So... it just depends on the age.

Due to my past experiences, the younger you are, the less serious "love" should be taken - though just the opposite happens.