Hello Big blue:)
I would say about 7 years maybe? But then again to be honest everyone matures in their own way and in their own time so I really think it just depends on how much they can get along and communicate no matter how many years apart they are. And also it depends on how much they love each other because one of them eventually will age faster than the other and might need a little bit more care, the only thing that would keep a person around to take care of someone who might be getting a little slower especially if they can’t feel their pain is love!
Love,respect, loyalty and understanding is all that is really important in a relationship 😉