Best time to mention?

[Falls Apart]

Nathan,

So, I've been writing books (if you count horrible ones I wrote with literally no experience) for about nine years now, have familiarized myself with industry terms/standards, and am currently about 25,000 words into a YA Horror book. I'm fairly confident about it, and even my most critical beta readers have been enthusiastic. At my current rate, I won't even be revising for a month, but I like to plan ahead. Whenever I consider the publication process, I always run into a significant roadblock. Specifically, how to bring up the fact I'm sixteen.
From all that I've heard/read, a query letter isn't the best time to do so. I don't want to seem like I'm presenting myself as some teen writer gimmick, not to mention the fact that opening with "Hi, my name is x and I'm 16 years old" just sounds downright tacky. I fully realize that I'd be competing with adults, and have no intention of submitting something that wouldn't be at that level. However, I also don't want to take an agent who thinks (s)he is dealing with an adult by surprise. I suppose my two main questions are, one, at what point should I mention my age and, two, would this be a deal breaker for some agents?
Thank you so much for any advice you can give me!

[Nathan Bransford]

I think it's best to mention it in the query. Opinions probably vary on that, but just as long as you let the agent know at some point you'll be fine. I can't imagine it would be a dealbreaker for any agent.

[Falls Apart]

Thanks!