I just wanted to write a reply because up to a few months ago, I was in exactly the same position as you !
Like you, I'm 15 and I've always loved to dance and had been taking street jazz and modern classes for a number of years but knew I wanted to dance professionally. I was sure there would be nowhere that would cater for my age especially beginner but there were so many and yes, some of the students in my class had been taking ballet for a few years and they were better but, I realised that I wasn't expected to be perfect just to do my best.
This weekend I did a performance for my Academy at a local Theatre and it was amazing !!!!
So I suppose what I'm trying to say is that just go for it. You obviously want to do it as you said it's a life long dream and Rome wasn't built in day, it's not perfection its potential.
Learning to dance is a whole new learning curve so embrace it. They'll be days when you hurt and ache and think I can't do this anymore but you're love for dance will pull you through.
Have fun and keep us updated
Never Give Up x