There is a operator at my airport that runs a 1983 CANADAIR LTD CL-600. and it is flying nearly everyday. They also have newer Challengers and a Gulfstream but the 83 gets a lot of time in the air.
I think for the most part charter clients do not inquire about aircraft age nor can/would they be able to really tell the difference between a 1983 or a 2017.
To most they just want to say they flew on a Gulfstream or show pictures of them in a large cabin jet. Just being honest.