Failed my PhD in Physics after 3 years in graduate school. I spent the whole first and a half year on foundation (courses and some learning projects) since I jumped in from a completely different field without any prerequisites. Then I spent another one and a half year on serious projects. I suffered in the second year due to the pressure from research and meanwhile, some personal issues which made me very very depressed. I failed a course (just could not work on anything at that period) and make unsatisfactory progress in research. And one can guess, failed qualifying exam. I left at the end of 3rd year without a terminal master, which is a large dent. If I apply immediately after quitting I will get rejected from all programs without problem. So, here is what I am thinking:

 1. I still love research and would like to devote to R&D as my career.
 2. I fully understand I am responsible for my failure and would like to deal with my issue.
 3. I am fully recovered and actually learned a lot from this about managing emotion and deal with pressure.
 4. I am planning to work in industry in related areas for a year or two or three, and during the time, keep looking for PhD openings. Taking exams, looking for research intern opportunities in my spare time. If lucky, I will go ahead and work towards a doctorate degree.

I have many concerns and therefore, need advices about this plan

 1. does this sound doable in general? I've seen people doing phd in their 30s or even 40s, but I know these are not the normal cases.
 2. What kind of job you would recommend if I want to go back to graduate school in near future? Or, what would be my best strategy? 
 3. How should I explain this part of my life to adcom when applying?
 4. I enjoy doing research and would like to pursue a R&D career in industry. But, just trying to see the whole picture, **is age a problem**? If I choose to do this and succeed, I will be in my early 30s to start phd and ideally, mid 30s to start my career. 

All advices are welcomed and many thanks!