Assuming you entered the name of an actor that has a corresponding Wikipedia entry you would be redirected to the actor's Wikipedia page that, in most cases, shows the actor's date of birth and calculates the age for you.

Even when I entered the actor's name plus the term "age" and was redirected to the Wikipedia search results, I could still see the actor's page as the third result and his date of birth in the summary text.

As for why anyone would want to search some things using Wikipedia versus Google, I can think of a few reasons. I cannot speak for other users however.

I have a script I wrote to search Wikipedia from the command line. For those who care, one can strip out "X-Client-IP" from the returned page html before opening the page in a browser.