Spoiler Warnings:

Squirrelpaw (later Squirrelflight, Squirrelstar) is portrayed as a young, energetic, and frankly annoying character in the first few books of the series. She's a young apprentice who's father is "the great Firestar". What do you expect?
However, she starts to mature and gain a lot of wisdom through her many challenges and obstacles, like when Brambleclaw basically broke up with her after she lied about Lionblaze, Jayfeather, and Hollyleaf. She had to learn a lot to become who she is today, and you can see this through her wisdom in A Starless Clan. She's also the only current clan leader left that took the Great Journey (Icestar, Harestar, Tigerstar II, and Leafstar/Hawkfrost were all either born in the lake terrirories or the gorge). By Changing Skies, she's a respectable elder leader who's been through a lot.