Coping with looking and sounding like a child in your mid 20's...?

On one side, I'm very pleased that I obviously look young for my age. That said, I'm getting tired of being mistaken for a kid and all the disrespect that goes with it. I'm 25 and most people guess me to be about 17. My voice - even worse - on the phone, I have been mistaken for my 6 year old step daughter many times. I literally sound like a small child and have lost count of how many times that has been pointed out to me, however politely it may be said. I once attempted to order room service at a hotel and the man on the other end baby talked to me and asked me if my mommy and daddy said it was okay... lol. Just a few days ago a man maybe 10 years my senior asked me what I was going to be when I grow up. When my husband and I go out, he is addressed as "sir" and offered a list of alcoholic beverages at restaurants, while I am addressed as "sweetheart", and offered a soda. (not sure what sort of illegal relationship they think is going on there... but he's only 2 years older than me). When I go into retail stores, I notice I am followed near jewelry and other small items as if I'm a 15 year old with sticky fingers. People who are younger than me talk down to me, and just about everyone treats me like a child, barely old enough for high school. I honestly have tried to remain positive about all this, telling myself that at least I know for sure that I don't look old yet, and won't for quite some time, however the way people often treat me because of it makes it hard to stay positive. I admit, I often have to resort to the junior's section for clothing since they often don't carry clothing in my size in the women's department, however, I never wear anything with childish decoration or labels. No tshirts, no bright colors. I wear only earth tones, and solid colors. The way I dress seems to only help in making people believe I'm a conservative teenager. Anyway, I guess I'm just asking for any advice regarding my situation. Maybe hoping to hear that someone else out there knows what it's like, or has a suggestion. I think what really sells it to people that I'm a kid is my voice, and I was never that insecure about it until, as the years passed, it became less and less age appropriate. I literally sound like a 1st grader. I've heard plenty of women with soft, or higher pitched voices, but they never seem child like, like mine, and frankly, it's depressing. I don't know... any thoughts?