Girlish, a.
Like, or characteristic of, a girl; of or pertaining to girlhood; innocent; artless; immature; weak; as, girlish ways; girlish grief. -- Girl"ish*ly, adv. -- Girl"ish*ness, n.
Shades of meaning
Fernald has no entry of its own for girlish; he lists it under youthful.
Where he writes about it:
Boyish, childish, and girlish are used in a good sense of those to whom they properly belong, but in a bad sense of those from whom more maturity is to be expected; childish eagerness or glee is pleasing in a child, but unbecoming in a man; puerile in modern use is distinctly contemptuous. — from youthful