16 is an EXCELLENT age to start in the gem business! I will assume you live at home, this is great because you are going to want to turn your profits into inventory and grow your business as quickly as possible, not paying for rent or food will be a big help!
Few words of advice:
A refractometer is your best friend in the world, along with some other basic knowledge of gems, it will ‘answer your question’ 99% of the time (maybe more?)
Subscribe to every trade email list you can, dedicate yourself to reading no less than two to three articles per day FOR THE REST OF YOUR LIFE! (I’ve been doing it for 22 years, I’ve missed days, but not many) This will only take 20-30 minutes a day and eventually, you will be the smartest gem person in the room in almost any situation.
High grade the best material out of every parcel, even commercial quality parcels, always put a couple/few of your best picks ‘away in the vault’, this is more or less ‘your savings fund’, you will be able to pick out the best of the best down the road, put $1000-$2500 into gold & diamonds to set it up, put it in an auction and when you sell it fifteen years from now for 20x your purchase price, it will feel like ‘free money’ 
‘The best gems always sell’ Super fine quality always sells, I had several dealers and jewellers balk at my price on this 8.65ct Tourmaline at the wholesale price! “I’ve never paid that much for a bi-colour tourmaline”
There is only one answer to that: ‘Because you have never SEEN a bi-colour tourmaline like THIS one!’
It sold yesterday because an East Asian client wanted to own it during lunar new year, he even rushed to pay me yesterday!!! 
