Hello,
Mechanical engineering is very interesting and will definitely help you in pursuing your chosen career. I studied mechanical engineering from secondary school (US: college) and I now have my Ph.D. in this very subject. I can inform you that mechanical engineering does not have any specific study on aerospace, however, the skills are transferable (you would need to modify formulas for the aerospace division). Textbooks about mechanical engineering are readily available, therefore, if you choose to pursue aerospace studies, you can study mechanical engineering in your own time to assist you with your studies. Some areas of mechanics are very easy and verge on common sense, however, I could assist if you have any specific questions.
I would recommend a university, however, they are all based in the UK and I assume you reside in the US. I will happily provide you with the information should yu require it.
Whichever path you choose, I wish you the very best in your studies.
Best wishes,
Josh