By element (suggested way) : Adds the element Date To Age in the same page where you want to calculate the age. Pass in the birthday and optionally a reference day. Then, use this elements age wherever you want. We also provide an event, so that everytime this calculation is triggered you can attach an event to it.
Server side: Simply add Birthday to Age action in your workflow. As this operates in the server side, it can take some seconds to process.