It's so funny to be reminded of that period in the 90s where any first person game was described as a "DOOM clone", because DOOM itself was the first FPS that hugely took off.
"The term boomer shooter has a rather nebulous origin, and it likely started as a joke. Online pedants often point out that the original first-person shooters were developed by Gen-Xers like John Carmack (born 1970) and John Romero (born 1967), not Baby Boomers. However, "boomer shooter" uses the slang version of the term boomer, as a stand-in for any older person who is closed-minded and out of touch—so please, direct those complaints elsewhere."