If you have any friends that use CAD programs a lot, buy them an age-appropriate drink and have them show you the basics. In my opinion, it's not so much learning a specific program (Solidworks and Inventor being based on the same approach, and being the widest-used) as it is learning how to approach drawing a part and turning it into a 3D part. I gained that ability by practicing reading drawings and reproducing the part in 3D. My high school had a textbook with a section full of such drawings. I also did a few models where I took an object I possessed and attempted to reproduce it in CAD.