I wear pigtails when it's really, really hot outside to keep my hair off my neck. I've been told it looks cute, but my hair is long, and it's more the hippie-style tails than the kid-style.
I think it depends on the context a lot. An older woman with fluffy pigtails and Hello Kitty bows, not cute. An older woman with neat braids dressed for working outside, sporty and possibly cute.