> For an espresso, 1-2 weeks old is totally fine (even preferred?), but for pourovers the flavor is totally different even just 8-9 days after roasting.

Most sources suggest that the optimum flavor profile develops about a week after roasting, and drinking coffee brewed from freshly roasted beans to be comparatively flat tasting. Blind taste tests have also suggested that contrary to the popular belief, beans don't go stale after two weeks, but retain the same taste profile almost out to 6 months (assuming proper storage). The key difference is that older beans are completely degassed, and pourover techniques and drawdown times as well as grind size should be adjusted accordingly, something hard to do in most espresso machines but easy with pourover. An immersion brewing method is also less sensitive to degassing.

Yup. Even after adjusting grind to account for age, i found 2 weeks to be cutoff for espresso out of my Silvia. I do pretty much only pour overs these days though, and find I need to adjust brew temp after around 8-9 day range. However, after 2-3 weeks I find the effort<>flavor trade off isn’t worth it, and toss the beans in a canister I keep for brewing with a Moccamaster.

Fwiw, I keep my beans in Fellow Atmos (vacuum) canisters. Picked up a 3 pack on sale at Costco, and I’ve been presently surprised by beans keeping a few days longer.

Not in my experience. I find some dippers to be more consistent process-wise than others, but to my palate, age of the roast is still the most important variable.