First I think you need to think about a direction. "Learn Math" is a very broad and vague statement. You will never learn all of math. So you really need to

First I think you need to think about a direction. "Learn Math" is a very broad and vague statement. You will never learn all of math. So you really need to think about why you're wanting to learn it, and pick a direction that suits that. If you're wanting to learn math just because you like the subject, then it's wise to get a sampling of a wide array of different areas. Then you have a better chance of finding an area that you like best. If you're goal is to learn it so you can apply it in some other area, you should focus mostly on learning what math applies in that area. Then find the prerequisites and start studying. Studying alone in your spare time will be nothing at all like attending a university. The full immersion you get to focusing primarily on one thing, and the ability to engage others at will also focusing on the same thing is a great help in learning. So set your expectations right. You won't be able to reach the level of understanding a 60 year old math professor has. Since he/she has been fully immersed in the topic for probably 40-50 years. So set your expectations accordingly.