You're in luck, there's actually a way to do that!
You should have a /etc/default/useradd file (or something similar). Within that file, I'm pretty sure you can set the following option;
This option actually sets when to flag an account as "inactive" after it's password expired, but hasn't been changed.
Note that this will only affect newly created users, and only the traditional "local users". If you're using anything like LDAP, you'll have to fall back on that documentation.
To retroactively change each user account on your server(s), you'll have to run the following command on each account.
chage -I <days> <account_name>
You can also view the current ageing setup for each user by running this;
chage -l <account_name>
Please note that you don't want to do this to *all* accounts on your system. Some accounts don't have passwords set, nor would they have password ageing setup.
Best not to mess with accounts like "bin", "sshd", etc.
Hope this helps!