If i'm diagnosed with hypothyroidism should i be worried? or is it something that's well treated? i'm 20 years old

Usually simple: If your thyroid is not making enough hormone you can usually just take a supplement once a day. They would want to decide why it happened, but it is not that uncommon. Once they sort it out it is no more a problem than remembering to shave (if you do) and having your blood tested once or twice a year to make sure you are on enough supplement.