Let's see... 10/2+8= 13. I don't see that as great.

Joking aside, I get where you're coming from, and particularly that there is no hard and fast rule, "half plus 8" is just a decent rule of thumb.

My wife is 11 years my junior. When I met her, I didn't think she'd be serious. After many years together, we both rarely think about our age difference.

In many ways, age is just a number. Your point about priorities (aka "values") is much more important.