Sheldon Cooper has shown remarkable growth over the first five seasons of Young Sheldon, but the character starts The Big Bang Theory without much evidence of that growth. Figuring out what happened, if anything, to slow or reverse Sheldon's social and emotional progress is a must for the show. Along the same lines, Sheldon on The Big Bang Theory has distant relationships with most of his family compared to the tight-knit unit shown on Young Sheldon. Season 5 left the family dynamics in flux though, so Season 6 will likely go a long way to rectifying the disconnect between the two versions of Sheldon. Changes in Sheldon are likely to come from himself, his family or will simply be glossed over.
Sheldon Cooper is a quirky and lovable genius who has difficulty dealing with social cues and social situations. The character was introduced on The Big Bang Theory, and Young Sheldon centers around his younger exploits and the Cooper family. At the start of The Big Bang Theory, Sheldon is portrayed as self-centered, awkward and isolated. Throughout the show, his relationships and emotions blossomed, and he ended the series in a much different place. The younger version has seen similar growth over the first five seasons of Young Sheldon as well.
Changes and stresses in Sheldon's family could cause him to become more withdrawn. George Sr.'s untimely death has always loomed over the series, but there is also infidelity on the horizon. George Sr. and Mary have a strained relationship shown in what is one of the more complex portrayals of a marriage in trouble on television today. Their troubles are likely to get worse as they deal with ostracization due to Georgie's baby and the added financial woes and stress that comes with changing jobs. Missy does a good job of keeping Sheldon grounded, but the pair will naturally separate as they get older. The one thing unlikely to change is Sheldon's strong relationship with his Meemaw, which has been a constant on both series.
Sheldon's changes could be largely internal. Sheldon is starting to worry more about the future. He has always been introspective, but even though puberty is traditionally played for laughs it is also a time of emotional and social growth. The next few seasons should see major changes as Sheldon is trying to find his place in the world. It could be that he will naturally distance himself from his family in Texas as he matures. Throw in the fact that he should be off studying in Europe soon based on The Big Bang Theory timeline, and his distance from his family at least makes sense.
One possibility is that the show will simply ignore the differences between the Sheldons and move on. While largely faithful to The Big Bang Theory timeline, Young Sheldon has made minor changes. Eliminating Sheldon's social growth seems like a major change, though. The show has been strong about sowing the seeds for Sheldon's later foibles so the writers are trying to fit in with canon. Young Sheldon has always highlighted Sheldon's more positive aspects. His behavior is already more palatable than Sheldon from The Big Bang Theory Season 1. Maybe the powers that be will not feel the need to completely wash away his growth on Young Sheldon and rather just live with slightly different portrayals.
The Big Bang Theory introduced the world to the flawed, but likable, Sheldon Cooper. The series worked in large part due to the ability to show Sheldon's journey and growth. The rule with shared media universes is to put the toys back where you found them when finished. The tragedy for Young Sheldon is that this means the show might have to break the character to put him back in his original state.
Young Sheldon returns for Season 6 on CBS this Fall.