login.defs password expiry
 

I had password expiry enabled by someone which would expire password in every 90 days. I changed /etc/login.defs not to expire password but the system still comes back every 90 days and asks to change password. Here's what I changed on my login.defs

Based on the man page, I think that those settings in /etc/login.defs only set the default values for newly created accounts, e.g. old accounts will still have the restrictions. You can use the chage command as root to change password expiration for existent accounts.