I've only just turned 21 and expecting my first baby! So as with yourself, I'm also considered quite 'young'. The thing is, years & years ago, many women our age would be married with kids by now without the intervention of modern medicine and scans etc, we are technically classed as being a healthy age for children as our parts technically in their 'peak'. Please try not to listen to old wives tales etc, they'll only make your worries worse! Being pregnant, you're also monitored very closely by midwives and doctors so if anything wasn't right, it'd always be picked up! You have so many blood tests, nothing could be missed!
Unfortunately, you're always going to worry, and there are always things you're going to question, when I found out I was pregnant at 4 weeks, I felt like everything went so slowly and worried about everything, I was constantly googling everything, and if I'm honest it only made things worse for me so I decided to have a break from the forums until my first scan! For peace of mind however, I'd definitely recommend booking an early private reassurance scan, I had one at about 8/9 weeks, then had my NHS 12 week scan, I also had a private gender 16 week scan and now I am about a week and a half away from my NHS 20 week! It goes by ridiculously quickly, so try and enjoy!
Always contact your midwife as well for any questions, you'll probably have your booking in appointment at around 8/9 weeks and they'll go through all of your family medical history, check your blood pressure, weight etc! Also don't hesitate to use the NHS website! There are answers for everything!
Please contact me if you have any questions though as we're both similar ages
good luck x