The movie takes place 30 years after the battle of Endor. Rey was born 11 years after Endor making her 19 years old. However, Ben, or Kylo Ren was born 0-1 years after Endor making him either 29 or 30.
[Sources of information: The book: The Force Awakens: The Visual Dictionary has details about Rey's age, 19, while I found Kylo Ren's age while researching through Wookieepedia (as unreliable as that sounds it fits with the appearance of the actor and timeline of the movie, in relation to when Han and Leia met... etc...)]