Hi!
I'm also a teenager. I signed with my agent when I was 17.
Don't get discouraged because of 1 rejection. There will be many. That's just how this business goes. Don't think that only some agents will take you if you're a teenager. My best advice is to leave out the fact that your a teeanger in your query. That part isn't necessary until after an agent offers. At that point, your age should be disclosed. (My agent didn't know I was 17 until she offered, and she told me that was totally fine.) The query and novel should speak for themselves.
I can't give you a list of "good" agents because there are so, so many. If I were you, I'd use AgentQuery or QueryTracker and search by your genre. That will help. Also, look in the acknowledgments of your favorite books.
I found my agent's name online.
I hope this info helps! Good luck!