First of all, good for you. Good on you for being 16 and being willing to work and not wanting to sit on Snapchat or an Xbox all day. If you were near me, I'd hire you to come help out on job sites right now.
Second, waiting until you're 18 is terrible advice (sorry @Newimage ). Asking questions and being cautious is great. If you can learn and do a good job, anyone who won't hire you strictly because of your age is a old putz and narrow minded. We need more young entrepreneurs.
What we don't need is more people running around with a pressure washer of any brand or GPM just spraying random crap without knowing what they're doing and what to charge. THAT is the main caution you'll get from guys on this forum, and it's a good thing. They want to protect their industry, and I'm for that.
@Innocentbystander is a grump, but he knows a thing or two. Only you know your area, but consider his advice. Conversely, if you've been asked to wash houses, don't be afraid to tell those people that you want to do the best job possible, and you're taking a month to learn as much as you can so you can do the best job possible.
Use the search function on this site and read the crap out of these forums. You'll get there.