7. The 'Ooh. Look, it's HIM / HER from years ago!'
Singular plot contrivances are not enough so subplot contrivances will be added in the form of casting some character actor from decades ago, who used to be quite well acclaimed early in his career, in some mentor role for either Boy or Girl character. Think Alan Alda/Elliott Gould/Donald Sutherland etc. They'll be on screen for the same amount of time that translates to no more then a day or two in front of the camera. They'll look utterly bored and lifeless but occasionally offer some line-reading that plays as an almost wink to the more cinematically-versed audience member that says "You should check out my stuff from the 70s. I was soooooo good then!"