1974, 1983, 1992:
In the DCAU there is no mention of Dick "Robin" Grayson's true age in the present timeline of the shows. During the flashbacks in "Robin's Reckoning, Part I" Dick Grayson is listed as Age 10:
But in the flashbacks of "Robin's Reckoning" it would seem that young master Dick is 9 years old, per the closing credits of Part II:
They can't both be right, as the flashbacks in Part II clearly take place after the flashbacks in Part I. So...which is it? Based on dialogue it seems that Age 9 is correct.
Dialogue from Part I:
"You deceived me. You can't take this one. Zucco's mine!." - Robin
"Sorry, Robin, but on this team, I call the shots." - Batman
"But I've waited half my life!" - Robin
This means that Robin is 18 years old in the present day scenes of "Robin's Reckoning"; 9 is half of 18.
The fact that 9 years have passed since the flashbacks is made even more clear in Part II:
This fits with Robin being in college as most people tend to graduate high school at 17 or 18.
"Robin's Reckoning" is set in 1992. It follows that Robin would be born in 1974 (18 years before these episodes) and that his parents were murdered in 1983 (9 years before these episodes).