Got to get a few years of physics and maths under your belt
first, well
before you can even think of doing astronomical research. If you can learn some astronomy while you are learning maths and physics, fine, but the main thing is to get that intensive quantitative background that distinguishes the professional astrophysicist from lesser mortals.
I think that, for most people, the additional effort of learning the vast edifice of astronomical science
at the same time as learning the necessary physics and maths, is much too much.
Witness all those astronomy PhDs who come out of their 10 years of scientific apprenticeship with no ability to do good research. Of course, there are
some people who are
smart enough to manage to get that rigorous physics and maths background, plus to also start doing good astronomical research, without scrambling their brains and then being unable to continue as a real scientist.
Physics and maths are vast subjects, and astronomical knowledge is also vast;
so my advice would be to focus on getting the knowledge you need to get, no matter how long it takes. There are too many burnouts and no-shows at the end of the "standard learning path" of a degree plus a PhD.
What I am saying is that the existing knowledge of stars and galaxies is now so vast that trying to get that settled in the mind
at the same time as becoming an expert in maths and physics, may not be desirable. It is perfectly OK, and probably the optimal path, to do maths/physics first and then start on astronomy later.
You have probably heard of the "ten year rule" , that is, that it takes ten years of intensive study to become an expert in a subject. But I think that for modern astrophysics, the learning timeframe may have to be extended to 15 years!
The standard path to becoming a professional astronomer is well described by Professor Duncan Forbes in the Following Document:
http://astronomy.swin.edu.au/~dforbes/mercury.pdf