How to cope with regret and shame about not fully utilizing opportunities during PhD? I am currently writing my PhD thesis and I was feeling guilty about the things and skills I could have attained during this period but I didn't. I have worked hard towards my research and have simultaneously worked on my hobby of painting and drumming during my PhD. Not that I joined a club or a band, I just studied art books, YouTube videos and practiced in solitude.

A bit information about me. I am not a brilliant student. Being average, I have struggled a lot during my PhD research as compared to my colleagues. 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. 

At the moment, my only skillsets are doing research (owing to my PhD), make somewhat okayish paintings,  drum somewhat, still love my hobbies and am a bit confident about presenting and public speaking owing to the conferences I have been to.

But, looking back, I feel like I should have invested my free time in meeting new people, learning more about public speaking, should have taken leadership positions and should have invested my time in doing things that would have improved my CV. In short, doing things outside my comfort zone.

How can I cope up with the regret about my failure of doing things that would have helped me academically and in industry? I am 30 years of age (fyi).
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.