A labeling age statement on American blended whiskey that contains neutral spirits (per Title 27, Part 5, Subpart C, Section 5.40) ordinarily refers only to the age of the 20% content of the product that is the straight whiskey used within the blend, and the neutral grain spirits used in the blend may not have been aged.
The company web site for Old Thompson refers to it as "4 Year Old Blended American Whiskey", and the picture of the label itself on the web site does not show an age statement, so Old Thompson is formulated from 20% 4 year old straight whiskey and 80% (un-aged) neutral spirits.
For example, there is no minimum percentage requirement for using some amount of higher quality (straight) whiskey in Canadian, Scotch, or Irish blended whiskey production, and as a result, such non-American whiskeys may often be made using a substantially higher percentage of neutral or near-neutral spirits.
The one substantial way in which such other countries are more strict than the U.S. is in the aging requirement, which is set at a minimum of 3 years in Canada, Scotland, and Ireland.
Under U.S. law, there is no requirement for aging of neutral grain spirits when these are used in a blended whiskey.