I don't know. I met a feminist once though who had 3 kids from 2 different dads and I think she was in her lower 20's. She was huge. She was bragging at work about how she dresses her son (I think he is 6-7) up in tutu's and stuff though. She claimed it was what he wanted to do but I seriously question that he was the one really wanting to dress that way.
Just looked up what maxi dresses are. Wow, such stunning dresses! It's a bummer if feminists feel like they are oppressive or something. Perhaps most of the self-identified feminists you found are somewhat tomboy-ish, so they aren't much interested in dresses.