My harley is going through his first molting right now. He's a little over a year. He present a lot throughout the day and has lost a few feathers. But his down feathers are everywhere. He also has pin feathers on his neck/head. I've been to that usually with molting, you'll see them lose feathers but never have a bald spot in one particular spot. That would be mostly be plucking. But harley is a little moody but still lives being handled and isn't stressed out.
As far as age, it usually depends on what breed of bird you have and will usually happen around the same time each year.