I was always surprised when I was really new to the world of credit how easy it was to get. When I turned 18 I immediately applied for a credit card as it would save me from having to borrow my mom's for online stuff. No questions asked, I got one. They would often send me offers to increase limit too. This is a good thing for anyone starting out at life, get a credit card, and use it! That's how you build up credit. By 23 I bought my house so I got a mortgage without needing a cosigner. Got a credit line around that time too and other loans as I had went a little over budget with renos. Now I keep the credit line as a buffer or emergency, I normally don't have a balance in it, but it kind of acts as a pay day advance, especially near the end of the month when a good chunk of the bills come out. Then I pay it off when I get paid.
Now days the only source of credit I may possibly need is if ever some huge expense happens like major house issue then I'd maybe ask to increase my credit line limit. But anything over 10k is going to take too long to pay off, so I'd probably open the mortgage at that point. That's what I ended up doing when I needed to redo weeping tiles, and needed a new car, all in one summer.
Interestingly a year or so after I had my house I checked my credit for fun and it was like 800 something, now I'm at 700 something. Odd that it went down, maybe because I'm not using credit as much as I was at the start?