I don't think there is likely to be any difference in the production quality of same model lenses with respect to when they were made. Having said that, older lenses will of course be well: older. Things like rubber wears out, tight joints become lose with use, etc. I have an a used 24-105mm, which works great, but shows its age. Faded rubber, has a fair bit of lens creep, ect. Having said that, if it's structurally sound, good lenses can last a long time.