The Big Bang Theory already answered Sheldon's biggest question on Young Sheldon season 6, episode 9. CBS' prequel spin-off returns after its winter break with an outing that continues Sheldon's attempt to get his grant database project. Due to East Texas Tech's meddling, the socially-inept genius is forced to raise funds for it himself, which means pitching the endeavor to possible investors. Following his colossal presentation in Young Sheldon season 6, episode 4, Sheldon comes up with an irritated query — something that The Big Bang Theory has provided an answer for.
Georgie's pregnancy news brought a lot of changes to the Cooper family which impacted the boy genius in both good and bad ways. He developed a fear of the future, resulting in Young Sheldon season 5's biggest TBBT tease — the debut of his first Flash shirt. Sheldon has moved on from that fear since then, but he faces a new problem as he struggles to execute what could potentially be a very lucrative project for him.
Cutting out East Texas from investing in his grant database endeavor, forces him to find financiers on his own. Sadly, no one would take him seriously because of his age, despite repeatedly explaining that he's a genius. Frustrated about the whole process, Sheldon asks Mary how long it will take for him to grow a mustache, so he could look older. His mother doesn't have an answer to this during the events of the Young Sheldon season 6 winter premiere, but The Big Bang Theory season 3 has already solved this when he debuted facial hair after three months of his Arctic expedition with Leonard, Howard, and Raj.
In The Big Bang Theory "The Electric Can Opener Fluctuation" episode, the boys return from their three-month North Pole trip. All of them were sporting full facial hair, including Sheldon, whose beard looked like the one Spock was sporting in the Star Trek: The Original Series' "mirror universe." Interestingly, Sheldon had the least bushy facial hair out of all his friends, which suggests that his hair grows slower than theirs. Regardless, their experience in the Arctic in The Big Bang Theory effectively answers Sheldon's query about how long it will take for him to grow a mustache in Young Sheldon.
Sadly, growing a mustache as he did on The Big Bang Theory won't solve the socially-inept genius' problem. There's no doubt that Sheldon is worse on TBBT than in Young Sheldon, which increases the chances of him behaving properly while fundraising. However, he just doesn't have the capability to be an effective negotiator not because he can be rude, but because he's too young to handle the matter. Negotiating a multi-million project demands a special set of skills. So while he and Dr. Sturgis may have found a financier, Sheldon's best bet is to recruit someone who can effectively sell the idea to investors while also advocating for his sake.