I'm nearly retired now, and I do think that one's motivation changes with age. For me, I will not now make a career of any subject I study, and university life is not part of the process of 'growing up' and 'finding my identity' in the way it was when I was 18. For me, the main motivations are the intrinsic interest of the subject and the opportunity it gives me to support my daughter in her - related - career.
Thinking about your motivations, you suggest two main reasons for doing this degree.
1. A wish to demonstrate a 'life lesson' to your grandson.
2. A wish to 'take something back' from institutions you feel did you a wrong.
There's nothing wrong with these motivations, of course! And I doubt I have anything to say that you haven't already done. But since you are currently struggling, here's some thoughts. First, you mention both your motivations in quite general terms - not specifically related to the nitty-gritty of the course you have chosen. Can you re-energise yourself by making a specific, course-related, goal that relates more directly to each of these motives? For instance - could you do project work/essays etc that identifies gaps in legal provision that led to your ill treatment by the Church or State? And how this could be remedied? Or could you choose options around family law and kinship/family care? (sorry this is a bit vague, I know zip about criminology!). I suspect that you have already done this, but perhaps the course requirements are pushing you in other directions? In which case, is it worth re-prioritising - deciding that you are doing this course to learn interesting/useful stuff rather than to get the piece of paper at the end?
Second, if he is interested, could you draw your grandson into getting involved in your degree - I don't mean getting him to do your homework (although....!!!) , but making some aspect of the course part of the discussions you have with him? That might help you feel a direct connection with your first motive?
Finally, have you connected with any other mature students who might be feeling something similar? Peer support can be so helpful...