Okay, well I took the comment as intending to mean 'teen musical' = about teens--- Bye Bye Birdie, Fame, Grease... Not 'teen musical', like is seeking teens as a target demographic--- Rent, Wild Party, Last 5 Years...
No matter which one you meant, there are successful musicals that can fall into both categories. Obviously, Spring Awakening is the best recent example, but there are others. And you have no idea what audience the 13 marketing is going to target... after all, Billy Elliot is based around 13ish year olds, and they won't court the teen audience aggressively, in my opinion.
Critics and audiences responding to 13 will probably not be swayed by their own views of Glory Days. In 1971, when Follies and 70 Girls 70, two musical involving 'old people', which is somewhat rare, opened within TWO WEEKS of each other, this didn't seem to have much affect on critical or popular opinion of either show. I think the same dynamic will be true in the case you're referring to. Did the level of success of Legally Blonde affect Glory Days? No, I don't think so.
[title of show] on Broadway. it's time. believe.