Geese: butcher at 9-11 weeks; 15-17 weeks; 22-26 weeks, for fewer pin feathers. If you feel under the breast feathers, you can feel the pin feathers if they are there.
Scald 145-155 degrees for 3 minutes.
My 2 year old geese are still growing, so I would consider anything under 1 year to be a young bird and would expect it to be tender.
My guys will be 5 1/2 months on B-day. They grew really fast and then the growth slowed down. I wanted as big a bird as possible, but the last 2 months probably weren't economical. They didn't really grow enough to justify the extra food they ate. But I don't care. I want an impressive show piece for my holiday table and I plan to give geese as Christmas presents to a few lucky relatives.
If someone had pasture for them so that they didn't cost anything to feed, it would be worth it to grow them longer for the few extra pounds. Buying all the feed, not so much.