What can I expect within a year? I've just started road cycling 1.5 months ago, I'm a 15 year old guy with no serious experience, my avg speed on a road bike is 16,8mph is that a good speed?, what can i expect in one year in terms of my speed?
You're still young - at 15 you are still growing, so work on endurance and technique, and not too much on raw power.
And remember its not about ultimate top speed, there's got to be an element of enjoyment too.  So work on enjoying your time on the bike, but also have a life off the bike.