Based on the wording of the presentation, the data seems to be from Nintendo Online. (See page 7)You trust picture doesn't even knowing what it means? Brilliant
Iirc there is a part in survey where you can specify info about children, their age and what they play.
But as with any survey a) this information is sensitive so many will opt out, b) people like to avoid complex stuff and many will skip this section (surveys usually simple and straightforward as people get quickly bored and try to avoid filling lots of stuff)
PS. Do you see an unnatural spike at 20yo? This is how it looks like when kids themselves participate and can't choose their actual age
They did an actual email survey asking about the age of the person in the household with "the strongest desire to purchase Nintendo Switch":

Nintendo survey reveals who's purchasing the Switch
According to a recent U.S. survey conducted by Nintendo, most Switch purchases are being made by "male consumers in their 20s and early 30s."