Currently for entry and another 180 stamp there is no need to show ongoing courses. If you wish to extend in country at an Immigration Office you will need to show this.
Not blacklisted as you woukd not be allowed in. Definitely looks like you have a note on your record though. Pal had similar coming up and down from Singapore where he was PR. Told to get a visa next time, not Visa Exempt.
You cannot get the DTV based on retirement. You would have to go Soft Power or Workaytion. You can get the DTV over retirement age. This is where maybe agents are getting confused.
Some agents have contacts. These are mostly Thai agents. If it was me I would only use a Thai Agent in a case like this. I doubt they would advertise these services openly.
If I was labelling him (PolSci Undergrad degree here lol) I would say right-wing libertarian with a few conspiracy theories thrown in for good measure.