Is it crazy that I want a roommate around my age?

[MTSUGURL]

So, I live in a pretty town home in Tennessee with a roommate, Andi, who is one of my closest girlfriends. It's been great - we're both on the same level of cleanliness, we have personalities that are similar and different in all the right places, we each respect the other's space and need for solitude at times, have similar sleep patterns, and share all expenses (including groceries.) We hang out together a lot, and it doesn't bother either of us that our Christmas tree is still up in the dining room.
The problem is that we need a third roommate. Her parents own the house, and they're currently paying the third of the mortgage that we're not covering with rent. Although we'd love to turn that third room into an office, she can't afford to split the remainder of the rent in half. We both work full time. She's 28, I'm 30, and we would really prefer to have another roommate that's not in college. Not that I don't love college students, but we would prefer to have someone that's also working full time, closer to our ages or older, etc. We just can't seem to find one. So in the next few weeks, we're showing the room to a few girls all around 20 years old. I'm a bit nervous. Our original 6 month lease is ending soon, and her parents have to put the house on the market if we can't find someone. (Her mother has cancer and the house is draining their savings.) I'm thinking it may just be easier for the two of us to move, but she's being really hesitant on that end as well. I just want to be assured of a place to live and not worry that it will be sold out from under me.

Help. Am I being awful to just really want a roommate close to our ages? I know college students can be quite responsible, several are paying their own living expenses, but we have such a quiet, peaceful place and I dread any changes to that.