Plenty of people take longer than four years due to reasons that would qualify them for protection from discrimination under the ADA. And as others have noted,

Plenty of people take longer than four years due to reasons that would qualify them for protection from discrimination under the ADA. And as others have noted, asking about this can also be construed as a roundabout way of discriminating on the basis of age. Sensitive (and smart) hiring managers would probably not probe that area too deeply. And honestly, I question the predictive value to job performance of this data point in the first place. I would hope most people wouldn't get hung up on it. There are many more valuable data points to examine.