Again, with the situation, it would have a lot to do with the actual relationship.
To me, and I'm going to get flak for saying this, age is just a number. I have meet dirty of boys who are 60 years old, who are just as immature as they were when they were 13 years old, and I have meet 15 year olds who are far more mature than people 20 years older than them.
Sure, in this day and age, there is a lot of immaturity going around. Me and Mel talk about it fairly often, because we both don't like what we see from behaviours from our perspective gender.
My idea of maturity in a relationship is, you are ready to live together when you are ready to take care of any children your arrangement will produce. Since there will be no children produced in this union, because she's got her tubes tied, I know this relationship is kinda immature. She wants all the benefits without any of the responsibility, and I assume she has been divorced once.
What will happen when her lover decides he wants to have children with her? There will probably be huge fights, and the relationship will break up.
So, I don't really see much of a future for this relationship.
And to all the people who say, this is creepy, get off your high horses, and stop judging people you don't know without all the facts.