I'm a 24 year old guy, and some people have spoken with me on the phone and asked if I have kids at home. They seem to think I'm in my 30s. I have a deep voice, but when people look at me, provided I'm clean shaved, they think I'm 18-19 years old, even though I'm 6'4 tall. So it's just my voice that seems misleading. But somehow, I don't think it has anything to do with how deep my voice is, because a lot of other people who have deep voices sound young, like in their 20s. What exactly is it that makes a person sound like an old man or old lady, and is it something to be concerned about? How can I make my voice sound as old as I am?

You can always see a speech therapist who can guide you. I tend to believe you speak with a bass tone so your voice is not only deep but probably reverberates which is certainly NOT a bad thing...AT ALL.

ETA: You may also enunciate very well which is also a great thing but can certainly be mistaken for someone more mature.