OMG at the pledge class mommy! SMH. You know freshmen are people, too. Some of them even are as mature as juniors and seniors.
Do it or don't do it, but don't go into it expecting that everyone in your pledge class will need to come to you, the two year older and wiser woman for advice. My class had women of all age groups, and you'd have never known it. We didn't focus on it. One of my best friends my freshman year was an alum in grad school that I am friends with to this day. Also, I was always really good friends with at least two or three of the new members from each pledge class. I wasn't their mentor or big sister; I was just their friend. This included my senior year with a freshman. You'd miss out on great friendships if age is a limiting factor.