Can I do a PhD after being out of academia for 5-10 years?
Why would you want to do the PhD? 

I don't ask this question to be nasty, but you really do need to know why you want to do it. I am currently working for a PhD in subjects that I have not studied or practised for 50 years (yes! 5-oh). 

I could not have afforded to interrupt my reasonably successful professional career to take on academic research that would not have enhanced my subsequent career, but, in my case, having ended my professional career I was free to pursue my academic interests. 

I know why I am doing it, and am very happy with that choice, but the crucial thing is to be really clear with yourself about your motives.