Thanks Brian. The first image is informative. My first comment is that adult ages were rounded to the nearest 5 years. An apparent age increase of 15 years between 2 census 10 years apart seems unlikely, but it's possible.
Anything you can add to the profile, even as a research note, could help someone else who looks at this question.
Lesley's answer (Denis, son of Denis, age apprx 1 in 1901) is consistent with the the census.