How to cope with regret and shame about not fully utilizing opportunities during PhD?
While sometimes it seems that spending more time working is equivalent to accomplishing more (especially in academia, where there's always that one colleague), this is not true in general. In particular for demanding intellectual work (as required in an academic environment) it is important to take breaks, vacations, and spend time doing other things to refresh ones creativity (see, e.g. Clark &amp; Sousa, How to be a happy academic, or any of the numerous articles online).

I personally like to look at CVs / personal websites of successful academics, and it is quite common that they have some hobby which has nothing to do with their work which they spend much time on, like sports, chess, music, etc. So you don't need to feel guilty at all. It's very common that people struggle during their PhD studies, everyone has to figure out for themselves how to "make it work". If for you that meant spending time in solitude, that's fine.


  This has led to spending a longer time on my research than my
  colleagues. It will take me a little over 5 years to defend. My
  colleagues and friends have taken somewhere between 4-5 years for
  their PhD.


So it seems you didn't actually take that much longer. Another reason not to feel guilty.


  I should have invested my free time (...) doing things outside my comfort zone.
  
  (...) I am 30 years of age (fyi).


Why not start now? At 30, most of your life still lies ahead of you.