As an alumnus of the University, current students feel more of an affinity with you than with any other professional.
Your success helps them to envisage their own success as a very real possibility.
Your involvement with current City students is not only of great benefit to the students but it can be of great benefit to you as well. It provides you with the opportunity to network with other professionals and build on your current skills. Volunteering also looks impressive on your CV as it is valued by employers. Many people who volunteer and work with young people find it an enjoyable and rewarding experience.