I think that being 16 is your biggest draw-back.
Even if it is a business, people understand you are still going to school and doing 16 year stuff, so they don't don't perceive any 16 year old having an actual business and taking it seriously. Ultimately they don't think a 16 year old has time for a business and think it's just extra money.
When I was growing up, I worked on my farm and was making more money weekly during the busy season than most part-time teachers. Some weeks I worked 40 hours +.
It's just a misconception that a young person can't or shouldn't have an actual business.
As for low-balling Dutch, we've all been there. When starting a business you need to generate income, and sometimes you might go a bit lower on a service just to get that income in the infancy of a business.
Anyone who says they never low-balled anything is lying. I'm sure that when starting any business, there has been times where they needed any income they could get so they might have priced something a bit lower than they felt comfortable with until they could actually establish their business and price things accordingly. I know I've done it in the past, and I wouldn't be surprised if I ever have to do it again, but with what I do, if I can provide a good price for smaller services, then usually it leads to bigger work.
Once you've got the client base and steady income stream, then the clients will request you specifically if you do quality work. At that point, you can charge what you feel is fair to you, and fair to your new clients.
I'm sure you have plenty of pride in what you do Dutch, but realize you are still young, so when people make comments that rub you the wrong way, just shrug them off and use it as motivation to make your business bigger and better.