In a section titled “The New Generation,” Hemmings last month devoted 16 pages to cars from the 1980s, ’90s and 2000s. “To some of us these seem like used cars,” the magazine said, “while to others they’re the stuff childhood dreams were made of.” The publication described the cars, which included American, European and Japanese models, as “a growing segment of the collector car world.”

Two years ago, Michael Caimano, who specializes in vintage cars for the New York auctioneer Bonhams, handled the sale of a 1995 McClaren F1. He said the vehicle had gone to a Gen-X buyer for $15.6 million, reportedly a record for post-1970 collector cars sold at auction. The transaction offers a graphic demonstration of the growing clout of younger buyers, said Mr. Caimano, 32.

“Close to half our sales are to that generation,” he added, referring to the McLaren. “They’ve achieved a position in life that puts them in the prime collection-building years.” At the same time, he said, “millennials are beginning to stick their toes in the water, particularly with midlevel collectibles in the $50,000-$200,000 range.”

Arguably the deepest dive into the trends sweeping auto collecting and investing comes from Hagerty, a firm in Traverse City, Mich., that specializes in collector vehicle insurance. Using its policy data, the company examined more than 18,000 transactions from 2016 through 2018 in which cars changed hands from older to younger buyers.

If one assumed that meant baby boomers (born from 1946 through 1964) buying from an older generation, that would be mistaken. Echoing Mr. Caimano’s experience, Gen-Xers (1965-81) like Mr. Glaubitz were the largest single group of buyers, accounting for more than 23 percent of the transactions.