@lamo, you could do it as outlined in the image shared below:
In the survey tab of your xlsform:
Data entry screen as seen in Enekto: when a date is entered outside a range
Data entry screen as seen in Enekto: when a date is entered within a range
Data entry screen as seen in Enekto: when a date is entered outside a range
Reference xlsform:
Constraint Age.xlsx (9.8 KB)