Young Sheldon Needs to Pack Up and Go While The Show's At Its Peak
Young Sheldon is a spin-off/prequel to The Big Bang Theory, which follows Sheldon Cooper, the future TBBT protagonist, at the age of 9 (at the beginning of the series), as he is living with his family in East Texas and going to high school.
While it is arguable whether Young Sheldon could have been successful without its connection to The Big Bang Theory, it consistently reaches the position of one of the highest-rated network series, and keeps going strong, currently at six seasons.
But however successful this series is, it has an inherent problem, compared to "normal" sitcoms – it cannot go on nearly endlessly. As seasons pile up, not only the plot is developing, but Iain Armitage, who plays Sheldon Cooper, is growing up. It is inevitable that quite soon young Sheldon won't be young anymore.
And the series seems to acknowledge that it cannot go on for more than one, or, at most, two additional seasons.
Young Sheldon started as something fairly removed from the original series, but recent episodes are seemingly setting up the dramatic background elements which The Big Bang Theory had revealed to us, primarily, the premature death of Sheldon's father, George (Lance Barber). George already had suffered his first, non-fatal, heart attack.
As the audience now got a chance to know George and love him, that tragedy is going to hit all the hardest. But his death also offers a good cut-off point for the series as a whole. Much of the plot had been centered about George and his increasingly troubled life, from his job problems to his complicated personal life. The situation which gave adult Sheldon his signature habit of knocking three times before opening any door is coming closer.
In TBBT Sheldon had disclosed that when he was 13, he came home from college for spring break to discover something unexpected and traumatic – and as the series is quite clearly directing George towards an extramarital affair with their neighbor, Brenda, it is clear what he's likely to find. And young Sheldon is 12 at the end of the last season.
The family falling apart, quickly followed by George's death from another heart attack, brought by new stress factors, and then Sheldon abandoning his remaining family and moving out for graduate school is the logical ending for Young Sheldon, which also establishes key character traits of adult Sheldon, like lack of trust.
Therefore it is highly probable that Season 7 will be the final season.