>One of the few regrets is that I didn’t learn advanced math back when my brain was primed for it. Learning calculus in mid-life is tough

in the same position. tried to get into deep learning last year and found my calculus knowledge lacking. If you're looking to get back into it efficently, checkout mathacademy.com. i'm currently doing it myself and I'm on track to make another stab at getting into deeplearning next year.