I got my first credit card at 18 years old - my first year of college. It at a $500 credit limit, and I still have it to this day; though the credit limit has changed to around $5K. This card is now rarely used - but I keep it for any work expenses that I incur that are reimbursable. It's the easiest way to keep things completely separate when I travel.
Jordan didn't get a credit card until just a few years ago when we realized is credit rating was in pretty bad shape. He didn't get a card as soon as he was legally able, and had a few dings from some early-adult rental arrangements that went sour. It took a few years, but we got him a secure card, and he used it diligently for a year before he transitioned to a regular Visa. He actually wound up cancelling it, because he found that he didn't use credit that was only in his name well - and didn't want the risk.
In addition to my personal Visa we now have two joint cards - an Amex where Jordan is the primary and a MasterCard where I am the primary. The intent here was to build our credit score/history.
Activity three of Level 4 is to request your credit history reports to see if the bureaus are tracking all of your good behaviour, and you haven't been the victim of either identify theft or just clerical errors. We did that a few weeks back, so they should be arriving in the mail any day now.