No cause for concern, that's the age I was when I noticed my first grey hair, 24 or 25-ish. If your parents had grey hairs at an early age, you're likely to get them young, too. No big deal, don't let them bother you. Think of those grey hairs as symbols of maturity & wisdom... and, if that is what they symbolize... well, then... I must be "wicked" mature & wise... 8)
You can get gray hairs at that age; It's not unnatural/unusual. Though, most likely, it will only be a few grays; your whole head of hair won't turn until your older. It can also be stress, lack of vitamins/nutrition, or sleep deprivation. It could also be genetic - early graying may run in your family. If it is a result of sleep deprivation or lack if nutrition/vitamins it could be a sign of some more serious health issues. You probably don't need to make a special appointment, but the next time you go in for a physical or to a doctors appointment be sure to mention it to your doctor.If you didn't intend on going to a doctor verry soon, you should probably make a special appointment - better safe than sorry they always say. If you've ruled out anything serious, you can try asking your parents/family if they got early graying. You can either accept the grays or if the look bothers you, you can dye your hair.
P.S. know, that early graying can also mean that ,if you do end up getting bald spots, it can happen early as well.
Hope you found this answer both pleasing and helpful. ( :