I am 18 years old and started building my credit the day I turned 18 by opening a secured credit card with Discover. I've been paying my Discover bill on time every month and in full. About a month ago I applied for an Amazon Prime store card and was approved. This week my Fico score posted (it takes 6 months of credit history to post one) with an almost 700 credit score and I checked American Express's website and they said I was pre approved for the Amex Delta gold card. I always fly with Delta when I go places (I often fly around the country to visit family) and was approved with a $1k credit limit. This is exciting for me because I love travelling and being able to earn miles is a plus! Anyways just thought I'd share.
Congratulations on your Amex Delta Gold approval!