When Was The Gospel of Luke Written?

I have been trying to search this on the web and it seems I keep getting conflicting information. Apparently, modern scholars believe the Gospel of Luke was written in the second century AD. If this is true then why do we include it in our Bibles? Why do people read it if it was written much later? And then, I read some info about it being written in the 60s AD. I tried to search this on StackExchange but no luck. Could you help me out?