Birthday ages show in iCal but not iPhone

Hi,

Having a brand new iPhone 4S I put some time in to move all my Google calendar and contacts over to iCloud, to get a nicely synchronised experience.

I used to have specific calendar entries for Birthdays but changed these to just adding a Birthday in each person's contact in Address Book. This works great, in iCal, on each date in question it shows a little present icon and says 'xxxxx's 20th Birthday'. Perfect.

My iPhone calendar, however, shows the icon and say's xxxxx's Birthday', no mention of how old they are.

The right Birthdate field has synced in contacts. Does this just not work on iPhones?

Thanks