What do I say to not sound like a ?

I'm 16 and I graduated highschool a year early. I'm also a very social guy and I go to a lot of parties and always meet new people and stuff. And it doesn't happen often, but when the subject of school comes up and I mention that I graduated early, people will often say things like "wow you must be really smart then" or things along those lines. I feel like if I respond with 'yeah I guess..' I'll sound like a or something. What can I say so I dont come off as a narcissistic h0le?