It sounds like you are talking about the "Died" line in the data fields at the top of a profile. For example:
Died before before about age 2 in St Pancras, Middlesex, England
As far as I know that "before about age 2" part is not user editable. It is automatically computed from the birth and death dates.
In your example it is technically correct, he was over 1 year old when he died, and that is all can be deduced from the birth and death dates. In your case you also have a record that says he was 4 years old when he died.
So you have a couple of choices:
- Just note the age at death in the biography
- Change the birth date field to be "about yyyy" where yyyy is the year that would give him an age of death of 4. The convention is to use "before the baptism date" but only if you have no further information about the birth date. In this case you do.