My other analogy for the Mt. St. Helens dacites . . .
This guy claimed he had this handheld sensor that could accurately measure a person’s age. I doubted its accuracy, so I asked him to go to the local hospital and measure the age of everyone in the nursery. He came back and said the average age was 5 years old. “Ha! Your device doesn’t work because the nursery has babies in it who are much younger than 5 years old,” I said to him. He smirked and replied, “You forgot about the nurses”.
The dacites have bits of old rock encased in young rock. That’s why they don’t have an age near zero.