I want to generate a binary variable name “eldest” as follows:

if a person is the most aged person in a household, then eldest =1,
if a person is NOT the most aged person in a household, then eldest =0

The command I used is as follows:

gen eldest=0
bysort hhid: replace eldest=1 if max(age)

by its says "Invalid syntax"

What is the problem?

What is the correct way to do it?

Thank You