It also allows you to choose if the result will display in years, months or days.
Keep the type as numeric and choose the calculate age icon.
By default years will be displayed. If you click in the field you'll then have the option to have it displayed in months or even days. You'll then want to select which date field you want to use for this calculation from the element drop down.
Once you're done editing the field (adding a title, description, etc.) click on the create button.
*Note: The editor is a powerful, advanced tool. It will take some technical knowledge (and definitely patience) to understand it. If you need help along the way, we are happy to point you to Knowledge Base articles and to provide quick responses. We also can make ourselves available for web training/help via our consulting services offering (chat with us to find out more).