I go to a lot of shows (and I set up and sell) and I believe younger people are interested in this stuff... and buying it.
One other thing you must remember, in my opinion, young people in this hobby should be considered around 40-45 years old and older. Because you have to think, at what age and stage in life does the AVERAGE person start to have a disposable income to buy $1500 signs, $1000 gas pumps and $250 oil cans?? You will hardly see a bunch of 25 year olds doing it. They just want to make their car payment. For the AVERAGE person who collects this stuff, it tends to be a ‘later-in-life’ hobby. After you get a job/career, buy a house, a cool car, etc etc. So the demographic of NEW collectors is already past middle-age in my opinion.
Of course there are exceptions, but this is my opinion.