It's both, Tim. The aeration and the warming both increase the volatile aromatics to reveal the flavor components.
As to your question about aging, that's more difficult. A lot depends on what you like in a Riesling. The Grossets should age for a good long time, many years, but will develop entirely different secondary and tertiary characteristics as they mature. You'll likely lose some of the fresh brightness that you find so engaging now, but then again, there should be a definite Riesling-esque petrol/diesel/rubbery/ foehn element in the older wines.
If you like that...and many, many people treasure it and seek it out...then that's fine. If you don't, you can always drink them up in early middle-age.
Me, I'd open a bottle every now and then to see how things were developing, and when I got to the point where I started thinking I couldn't possibly enjoy them any more than I did at that moment, I'd start gorging myself on Grosset! But that's me.