Do you already have an undergraduate degree? Did you take some basic science courses during the course of that degree? Or at least, some math? I ask, because you may not need another undergrad degree to proceed. (or, it might be quite accelerated, if you get credit for some classes, at least) It's quite common for MBA students, for example, to have a few undergrad "core courses" before moving directly to their graduate degree. I have an engineering bachelors, and had a handful of classes before beginning my MBA.
In terms of awkwardness, I think working with younger people can be very energizing. And you will be aghast at their lack of discipline. But you don't have to give them allowance or get them out of bed, so there's that.
In terms of working in a graduate degree, it depends on the school but I think you will find quite a mixture: second careers, as you have; ex-military on their GI Bill, people who took time off for kids. No big deal in grad school.