This is yet another milestone to brush off the last bits of baby/toddlerhood, and I say, thank goodness! I'm so excited she has this in her rapidly growing big-kid repertoire.
Not sure where this fits into stereotypes, but Katrina was well behind her brothes in relative age giving up training wheels. Julian was 3-1/2, Gabriel was 4-1/2 and Katrina was 5-1/2. Just a data point, and in our case probably mostly dominated by personality -- for instance, Julian had no POINT to prove when he was learning, he just wanted to learn to ride, and did.
In any case, I'm thrilled they're all on two-wheelers now!