On the wikipedia website, it says that Teresa's bday is May 18, 1972, making her 39. It doesn't give a birthdate for Melissa, but I've read a bunch of places that she's 31 or 32.
Teresa absolutely looks much older than Melissa. This is my first season watching - always had heard what a following Teresa had, so I was surprised to find I really dislike her. I know we don't see everything going on, and I guess her attitude can of course be related to all the financial and legal crap she's going through, but wow, I'm not a fan at all.