Well I'll tell you what I'd tell anyone else, animation is a terrible career choice right now. Schools are churning out boat loads of animators and there's no jobs! Getting that first job is becoming impossible outside of Asia and even there, they're not in high demand. For someone who hasn't even started, it's not adviseable. There are tons of insanely talented artists, artists I know, with experience in major shows or games who can't get jobs even when asking for wages that barely match mine and I do just above entry level work! I work in VFX so I have a lot of animator friends. Many have quit to go back to school, are doing evening courses for something else or just unemployed and depressed.
However, that being said, what exactly would your plan for ballet be? Like you've pointed out, you've not bring doing it that long so you're at a disadvantage and unfortunately highly unlikely to be much competition compared to those that have been doing it since they could stand. For example, at 15 most athletes had already been scouted, were aiming for scholarships already or playing for feeder teams having trained most of their lives. They're not just starting then. I'm not trying to burst your bubble, it's awesome that you love something so much but whereas I could see what you were thinking with regards to a career in animation, I'm not sure what your future plans would be with regards to making a living from doing ballet unless you maybe want to teach. Is that likely to be in high demand? And I think that has to be the decider for you.
There's always ways to continue something you love more as a hobby. I live for Taekwon-do and I want to continue with that and teach. I train every day and attend class 3 times a week but I also have a full time job & went to school to get the qualifications for that job while keeping up my training. From what you're saying, I think you should always do what you love, but without a way to make a career out of what you love, it's perhaps more advisable to continue it more as a hobby on top of real work. Not just in terms of finances but also because anything like ballet is a short lived skill. It's all downhill getting into late 20s.