You can do this but you first need to populate the Birthday field in your contacts.
After you have done this, go to Google Calendar:
- In the left hand pane click
Browse Interesting Calendars
- Click the
Contacts' birthdays and events
Back to Calendar
IIRC, the Google Calendar doesn't provide notifications for these events.
To receive notifications you will probably have to use a Third Party Application - one of these Apps being http://contact-birthdays.appspot.com/ ( I haven't used this application I found it via a Google search)
Sorry I missed probably the most important part of the question - I am pretty sure you can't display the age. This feature request has been outstanding for quite some time now. There is this userscript that adds the age to the event.