The biggest difference for am and juniors in club fitting is the amount of change a junior can go through. If you have a big clubhead speed increase or junior growth then you need new clubs and fitting. If not much has changed in your swing or game you can wait.
The biggest issue most players make is buying right off the rack or off eBay. You can get what seems like a deal but the clubs shaft is not as labeled or wrong clubs for you. It’s much better to spend some money and get properly fit by a good fitter than to try and save money. In the long run buying equipment that isn’t right for you.