Yes, The MLP fandom has grown, and Yes, our numbers have increased. But like with every fandom, this will naturally happen. I'm sure that people were asking this question 4 - 5 Years ago.
Look at the Anime and Manga fandoms, EVERYONE that is internet literate is part of one of them, Yet they don't mind! We should embrace the changes. Not resist them.
Also on the matter of MLP being a mature fandom, The bronies that created the fandom, and those that keep it running we obviously mature people. We are the most tolerant, caring, intellegent, and loving fandom out there! Its the people that make us up that matter.
"Change is the law of life." -John F Kennedy.