Hi, maths is not my area either...
Actually, I just want to wish you the very best with this and say Good Luck as it seems your heart is really set on it.
I would say, in order to achieve what you want to achieve, 6 months sounds reasonable- especially as youāve planned how you will carry this out.
Stay focused and motivated and look for tips about how to remember certain things. This could be developing your own learning/revising system, perhaps means of triggers- for example- post it notes around your home which make you think about key topics. Well, I found it helped me in my studies but, again, I wasnāt studying maths!
Good luck and I hope you come back to inform us of updates.
There are people here who Iām sure will offer you some good advice.