how to set individual session maxAge in express?

You can set either expires or maxAge on the individual cookie belonging to the current user:

// This user should log in again after restarting the browser
req.session.cookie.expires = false;

// This user won't have to log in for a year
req.session.cookie.maxAge = 365 * 24 * 60 * 60 * 1000;

See connect session documentation.