youthful, immature, inexperienced
As a fledgling professor, I would sometimes embarrass myself by making mistakes in my lectures which even the students noticed.
fully fledged = mature or experienced, but fledgling means the one who isn't matured, i.e. is a neophyte or newbie rhymes with duckling and a young duck is inexperienced. sounds similar to sledging in cricket: Normally inexperienced young players do sledging if they are unable to get wickets.