Sam, you have asked the very question I was planning to ask! After trying the fabulous aged Gouda from Murrays that you sent me ... wow, simply incredible.
I have only recently, in my last couple of Gouda makes, succeeded in getting results that are on target. Early on I tried Gouda a few times, and I always got results that were crumbly and more like a semi-cheddar in taste. (Tasty cheese, but not Gouda.) Turns out I was leaving the cheese in the press too long, allowing the cheese to get too acidic. It was quite some time after I got a pH meter that I tried making another Gouda, and I discovered, when I tested the cheese as it pressed, that it hit the target of ~5.3 far, far faster than I would have expected - while the washing "resets" the pH by way of dilution, and presumably has some effect on the rate of acidification by way of reducing the lactose, my experience suggests that washing doesn't necessarily prevent the cheese from acidifying far too much. But when I put the cheese in the brine at ~5.3, I got a smooth, flexible, mild cheese - Gouda!
I've since made another Gouda, but it still has some ways to go in aging just to be a regular Gouda - and I don't think it would be a good candidate for long aging, because it came out relatively high in moisture. Like you, I'm guessing that one of the keys to a long-aged Gouda will be to aim for a rather dry curd. This would suggest shorter flocc, smaller cut, longer stirring, higher heat (though can't get too high, since this is mesophilic) - all while making sure the pH doesn't get out of hand.
If anyone has made aged Gouda, or has a recipe specifically for it, here's at least two of us (Sam and I) who would love to see it!