In S02E22 "A Swedish Science Thing and the Equation for Toast", Dr. Sturgis had a nervous breakdown when he realized that he would never win a Nobel Prize.

Mary told Sheldon about this in S03E01 "Quirky Eggheads and Texas Snow Globes".

• Young Sheldon S03 E01 - Dr. Sturgis Taken to Mental Hospital

• Young Sheldon S03 E1 - Sheldon Argues about his mental health

Dr. Sturgis spent some time recovering in a mental institution and returned in S03E05 "A Pineapple and the Bosom of Male Friendship".

When Sheldon's grant database project failed - his first big failure - he was distressed and wanted to quit college. In S06E15 "Teen Angst and a Smart-Boy Walk of Shame" Dr. Sturgis cheered him up.

Dr. Sturgis: "Well, good morning, Sheldon."

Sheldon: "What's good about it? I'm a laughingstock."

Dr. Sturgis: "I don't think anybody cares."

Sheldon: "But my database failed."

Dr. Sturgis: "Failure only means something if you quit."

Sheldon: "Well, get ready for some meaning. I quit."

Dr. Sturgis: "Hang on. Are you familiar with the Fred Astaire song 'Pick Yourself Up'?"

Sheldon: "No."

Dr. Sturgis: "From the beloved musical 'Swing Time'?"

Sheldon: "Still no."

Dr. Sturgis: "Then prepare to be uplifted."

Dr. Sturgis sings:

♪ Nothing's impossible, I have found ♪
♪ For when my chin is on the ground ♪
♪ I pick myself up ♪
♪ Dust myself off ♪
♪ Start all over again ♪

Sheldon: "I'm not uplifted."

Dr. Sturgis: "Well, then buckle up for the second verse."

Dr. Sturgis sings:

♪ Don't lose your confidence if you slip ♪
♪ Be grateful for a pleasant trip ♪
♪ And pick yourself up ♪
♪ Dust yourself off ♪
♪ Start all over again. ♪

Side notes:

Sheldon cried because his neutrino hero Frederick Reines didn't win the Nobel Prize and because no one came to his party, emphasizing his loneliness: 'but in that moment, I felt like a neutrino, destined to be alone forever'.

Leonard was 10-years old, Howard and Raj both 9-years old , Penny 4-years old, Bernadette 5-years old and Amy 10-years old.

I think Penny was supposed to be more than 4 years younger than Leonard, but thanks for clearing that up. I had gotten the impression from the season 2 finale that Dr Sturgis had a more serious problem.

@Knixon said:

I think Penny was supposed to be more than 4 years younger than Leonard, but thanks for clearing that up.

You're correct about the age difference.

Nobel Prize in Physics for Jerome I. Friedman, Henry W. Kendall and Richard E. Taylor awarded on 17 October 1990.

Leonard (May 17, 1980): 10 years and 5 months old.

Penny (December 2, 1985): 4 years and 10 months and 15 days old.

Age difference: 5 years and 6 months and 15 days.

Within the show, seemed like the age difference was supposed to be more. Otherwise why tease Penny about marrying "an old man" if Leonard was only 5 years older?

Maybe I'm wrong but it still smells like a retcon to me: they just wanted to show a childhood Penny in that "flash-forward" scene, and threw the previous canon out the window to do it.

@Knixon said:

Within the show, seemed like the age difference was supposed to be more. Otherwise why tease Penny about marrying "an old man" if Leonard was only 5 years older?

Penny was flirting with the Maitre d’ at the restaurant to get a tabel. Usually that works, but this time it didn't. He called her 'Ma'am' and she realized how old she looked at 30.

• S09 E15 "The Valentino Submergence (Feb 11, 2016)"

Afterwards Leonard was teasing her and she tried to get back at him, which didn't work. He didn't mind being called 'an old man'.

Penny: "Can you believe when I met you I was 22? I mean, it’s crazy. Where did all that time go?"

Leonard: "Hmm, you watched 'The Bachelor a lot'."

Penny: "Yeah, go ahead and make jokes, but your thirties are almost over."

Leonard: "No, they’re not."

Penny: "You’re closer to 40 than you are 30."

Leonard: "Ha, ha. You married an old man. Tell you what. Let’s do something fun tonight."

Maybe I'm wrong but it still smells like a retcon to me: they just wanted to show a childhood Penny in that "flash-forward" scene, and threw the previous canon out the window to do it.

I don't think the ages are a retcon. This is a season nine episode, written in 2016 and no one knew then that the show would end in 2019 with season twelve.

There seems to be retcons and inconsistencies in "Young Sheldon", but this is disregarded with arguments, like 'Sheldon is an unreliable narrator, he tells it in his own way, and even with an eidetic memory he was still a child then and might not have interpreted the situation correctly'.

Okay, but that might make my case. If Penny was 22 in season 1, then in season 9 - 8 years later - she would probably be 30. If Leonard was "closer to 40 than 30" at that point he would be at least 36, which would make their age difference 6 years more likely than 5.

I suppose it could still be close though, which could mostly mean that the "old man" thing was the exaggeration.

It might also be possible that Penny was younger than 22 at the start of the show. I'd have to go back to when she talked about first coming to California and how long she'd been there. Her saying she was 22 then, in episode 9, may not be dispositive.

Kaley Cuoco's birthday - November 30, 1985 - was used. Only the day was changed to December 2.

Okay then, Johnny Galecki was born in 1975 which makes Leonard 10 years older than Penny, so neener!

Nah, I mentioned that coincidence, because it's something I noticed back in 2008, when I saw the episode "The Peanut Reaction" (S1E16, 2008) about Leonard's surprise birthday party.

After that episode, I looked up the actor's and the character's birthday. Galecki's character Leonard was written as 5 years younger than the actor. Sheldon's, Howard's and Raj's birthday then was unknown. I assumed that the birthyear would be about the same as Leonard's: 1980. Then I noticed that Kaley Cuoco and her character Penny had the same birthday. I thought it was a joke or 'placeholder', as actors and the characters they play usually don't have the same birthday. But it hasn't changed since then, except for the day moving from November 30 to December 2.

So, it seems like the writers stayed with Kaley Cuoco's birthday and have the other main actors play a younger character.

Which means the "Hah, you married an old man!" thing just didn't really hold up.

That was just Leonard teasing Penny, when they were going back-and-forth about getting older. He didn't mind being called old, while Penny did.

I suppose. She was like 34 at the end, maybe closer to 35.