Welcome to the community @swill123! Try this (it should solve your issue):
if((${age}<1),'0-11 months',if((${age}>=1 and ${age}<15),'1-14 years',if((${age}>=15 and ${age}<20),'15-19 years',if((${age}>=20 and ${age}<=24),'20-24 years',if((${age}>=25),'25+years','')))))
In the survey tab of your xlsform:
Data entry screen as seen in Enketo:
Reference xlsform:
If Statement.xlsx (9.6 KB)
