Reddit reviews Applied Survival Analysis Using R (Use R!)

It might be a good idea to try and follow something approaching a university curriculum for maths.

For example, my undergrad curriculum went something like this:

1. Calculus I (this was most a catch up sort of course, revision from A level stuff, but it began to go into differential equations and partial differentiation which I don't think is covered at A level);
   
   
2. Linear algebra I and II;
   
   
3. Statistics I and II; depending on how much you like stats, I guess, but it's pretty useful to have at least some background in this.
   
   
4. Mechanics; if you like physics, probably a safe bet here.
   
   
5. Discrete Maths; set theory, etc. This was one of my favourite modules in my first year.
   
   
6. Vector Calculus; once again, if you like physics...get up to scratch with calculus first though.
   
   
7. Calculus II; sequences, series, Taylor series, power series, all that fun stuff.
   
   
8. Real Analysis; everyone moans about this one but honestly, I found it super enjoyable. It's where you really get into the theory behind some of the stuff you've learned in calculus, proofs etc.
   
   
9. Differential equations - ODEs (Ordinary Differential Equations) and PDEs (this was an optional one for my course, Partial Differential Equations, but it follows on from ODEs, so...).
   
   
10. Graph Theory; this one could probably go right after discrete maths, and it's quite fun again, I think. I wasn't super interested in the topic by itself but I enjoyed the module anyway.
    
    
11. Complex Variables; fit this in somewhere after vector calculus, I'd say, although you could do it earlier, after calculus.
    
    The other modules I took were Survival Analysis, which pretty closely followed this book , but may not be of much interest to you, and several operations research based modules: Linear Programming, Nonlinear Programming, and Combinatorial Optimisation. I really enjoyed Nonlinear Programming the most out of those, although doing the other two helped with that.
    
    I also had some intro to computing type modules, learning to use MATLAB, R and Maple (seriously, learn to use MATLAB if you can; Octave is a free alternative); Python is also good to learn. There were some "general skills" type modules too, looking into number theory a bit, and a dissertation, of course, which involved choosing a subject and researching the hell out of it, then trying to make something of it.
    
    I mean, this is a very broad overview. I'd recommend looking at some course structures on university websites and following them in terms of subjects - start with first year, of course. You may have to study a few things you don't like too much, but you'll miss them later on if you don't follow them (seriously, I hated differential equations when I first met them, it wasn't taught well at all and the notes were awful - but they're pretty damn important).
    
    Suggestion: you can apply for a student loan at any age if you've not had one before. Consider going to an actual uni if you're really interested in it? I didn't do A level maths, I did some courses with the Open University instead, which was enough to get me in to uni. Speak to uni admissions hotlines to see what they'll accept.
    
    And finally: do you have any sort of goal to work towards? Is there an area you'd like to one day understand/work in? You can tailor your choice of what to study based on that, if so. If it's just general interest, I'd suggest following the undergrad curriculum idea (mine or pick some unis and look at theirs, they'll all be fairly similar, might have different names for courses or break them into smaller pieces than mine did).