Find out an actor's age by going to the celebrity's IMDb page; if the information is not listed there, Wikipedia is another source where an actor's age may be found. There are several different "favorite actor" lists that have been created within the IMDb database also, with most showing actors' birth date.
Wikipedia usually lists actors' birth dates, as well as other vital statistics. This database also has several lists created of popular or award winning actors which includes their ages, such as "List of Academy Award Best Actor Winners by Age."
Another great source for finding out an actor's age, as well as marital status, number of children and movie or television credits is Biography.com. This source also provides a short biography of the actor's life and, in most cases, an interview with the popular idol.