Just accept it. You're going to be an adult who just has a higher voice, like that comedian from America's got talent last year. or whenever (Drew Lynch). Right now, you're still in your grace period before you actually look like an aged adult. Everyone's age where they start aging hard is different, very soon you'll look 30 and people won't have this confusion anymore. So, your problem is temporary.
You will always sound like you're talking deep on purpose, there's no way to make that sound real. Everyone will notice, but nobody will tell you they notice, so you'll just be embarrassing yourself if you try to deepen your voice.