Recently (~2 months ago) I decided to start self-teaching myself mathematics again, having last formally studied it when I was only 16 (I am 30 now).
My goal is to spend a little time doing it every day, not to attain any specific qualification, only to "learn maths".
There are lots of online resources, though it's hard to know where to begin or to go. "What interests me" is difficult because I don't really know the answer yet.
I have been following some of the GCSE syllabus, effectively re-learning what I studied at school (today it was completing the square), but I'm not sure if I'll find this motivating enough.
Now, What do You mean to "learn Math". You have to be more specific with your goal. This is funny coming from me because I haven't able to specialize in any single topic.
Let's suppose You somehow saw The Beauty of Math somewhere and You are ready to continue your journey in such a beautiful topic.
I really believe You Will enjoy reading "Mathematics for The million" by Lancelot, I saw this recommended by Sir Anthony Hoare[2], You Will be amazed by its content (I have only ready chapter one).
What's Mathematics?
Are elementary school children doing Math when they solve addition and subtraction problems?
Is The High school student crunching mechanical procedures, plugging numbers into formulas doing Math?
Is theorem proving Math?
Daphne Koller said in an interview that we are all doing probabilistics when Thinking and making certain decisiones[3]. Are we all Mathematicians?
Do You want to study Math as a tool to help You in some other areas or study it itself as a subject?
It doesn't matter, You Will enjoy it and love it.
Trying yo answer your question. Learn some Arithmetic, just enough. Crunch some elementary algebra (in The fashion of Visualizing Algebra provided by Udacity). Read The book Geometry by Tatiana Alekseyevskaya, learn some Discrete Math (I recommend You the book on the topic by Thomas VanDrunnen), read the other four books in the gelfand series. Learn some logic. Read Introduction to Mathematical Thinking by Keith Devlin. I think at this point You Will able to read some resources o calculus or abstract Algebra.
If this seems like a Lot, don't dismay. There was this guy George Green having to take care of mill to make bread and do also found time for Mathematics, apparently DeMoivre was struggling financially. There people are just like You. Enjoy your Math journey
[1] The interview is available on Lex Fridman YouTube channel.
[2] The conversation between him and Leslie Lamport is available on YouTube