What is the right age to introduce kids to our epics? Or it is not required at all to introduce them to mythology, considering the fact that we don't know it existed in reality or not?

IMHO, it's a very personal choice. You're not bound to introduce your kids to mythology if you wish. I know of one friend who got confused between Lord Ganesha and Lord Hanuman -- I haven't seen a more sorted out person then her. Probably putting facts as they are instead of asking kids to believe stories inculcates logic in them and they don't take things for granted. For example, the child might learn that unlike in epics, good doesn't always triumph over evil in real life. It also teaches her to believe in the self instead of putting her belief in an unseen force. Having said that, it's a personal choice and you have to make sure you're not hurting your beloved ones in the process :)