The Golden Age is a collection of childhood reminisces. I don't think there's any better way of describing it. It's an anthology of short stories about a childhood spent in the English countryside that clearly was influenced by Graheme's own childhood.
I spent part of last year reading A. E. Nesbit's Bastable books and it's hard for me not to compare the two works. On the surface, they seem pretty similar. A group of English siblings having misadventures. But the Golden Age is from the viewpoint of a wistful adult looking back while the Bastable books as from a child's viewpoint.
I have been fairly harsh on the Bastable books. Those crazy kids don't seem to ever learn from their mistakes. But I have to say they are the better books. Oswald Bastable's narration, full of brashness and totally clueless, is a great literary invention. And the scrapes the Bastables get into are several levels higher than the scrapes in the Golden Age.
The Golden Age does do what it sets out to do. It perfectly captures an adult looking back at dreamy memories of childhood with a profound sense of distance and loss. It becomes downright mythic when he compares the distant adults to Olympic gods and muses how he may have become an Olympian himself. The Golden Age is ultimately a very melancholy book.
The Bastable books are written from the view point of a child for children. The Golden Age is about childhood but it isn't written for children. I may very well read the Story of the Treasure Hunters to my son when he's older but I don't see myself reading him The Golden Age.