Hiroyuki: Long time no see, little buddy! Have you been a good boy while I was gone?
Shun: H-Hey! I'm not a kid anymore! I turned 18 last month!
I let him go with a chuckle. Shun was always the youngest in our circle of friends.
Annie’s pretty young, we try not to sexualise her.
— Jeff, Community
"This TMNT iteration put most of its attention on depicting a modern family. Naturally, I feel like Mikey's character really represents this almost overlooked dynamic many youngest siblings hold that is present in a lot of families.
"Being the youngest, Mikey is coddled more and treated with more sensitivity than his brothers. This is shown through the others' dynamic with him throughout the series. For example, you may notice Leo, Donnie, and Raph don't really rip into Mikey in the same way they do with each other while teasing. The older brothers are always looking out for Mikey in their own ways. Mikey never had the pressure to contribute to his family in the same way his brothers did.
"In 'Donnie's Gifts', Donnie makes an inflatable suit for Mikey so that he won’t hurt himself jumping around. This is a gift that noticeably annoys Mikey, as it gets in the way of his fighting style, which is very hyperactive and flashy. More specifically, however, he's upset by the prospect of Donnie feeling the need to baby him. (…) He doesn’t like being held back because his brothers are too concerned with his safety. It may be why he goes for such a— as he puts it— "razzmatazz" approach to fighting. He wants to prove he can do things without the intervention and supervision of his brothers.
"Raph is significantly more overprotective of Mikey than he is over his other brothers. This is a dynamic that seems to have a lot more depth than we are shown within the series and the only time it gets much focus is in the episode 'Hot Soup: The Game'. In this episode, Mikey decides that he is going to go on his first solo mission in order to retrieve a Lou Jitsu game from an auction house. Raph is the only one of his brothers that seems concerned at the idea of this. His concern greatly annoys Mikey throughout the entire episode, leading to Mikey making a few passive aggressive remarks towards his older brother.
"During Mikey's mission, he continues to bring up needing to succeed in order to prove to Raph that he is capable of doing things on his own. This desire to stick it to Raph isn't new either. There are quite a few small moments in the series that depict this slight tension in their relationship as far back as the first episode, where Mikey steps forward after Raph's failed attempt at opening the hidden mystic doorway and takes pride in managing to succeed where Raph didn’t. (Important side note: there aren't malicious undertones in this behavior, it's simply a petty 'gotcha' for Mikey to say 'See, I can hold my own just fine. I don't need you all the time.')
(…)
"I could probably go on and on about the little examples of this sprinkled throughout the show, but I think that would be redundant. Through all of this, it is easy to tell that Mikey hates being babied and treated as if he is incapable solely because he is the youngest in the family. He wants to feel as useful as his brothers and be able to protect them and be there for them in the same way that they are for him. As many youngest siblings do, this makes them desperate to be seen as an individual. He becomes more ostentatious with his self-proclaimed "razzmatazz" to draw more attention to himself in fights in a subtle act of rebellion against his brothers' overprotective attitude towards him. Especially towards Raph. Mikey actually appears to distance himself from Raph the most due to him feeling as though he needs to prove himself as independent to negate his overprotectiveness, whereas you will see him regularly clinging to Leo or Donnie for emotional support."
"Being the youngest, Mikey is coddled more and treated with more sensitivity than his brothers. This is shown through the others' dynamic with him throughout the series. For example, you may notice Leo, Donnie, and Raph don't really rip into Mikey in the same way they do with each other while teasing. The older brothers are always looking out for Mikey in their own ways. Mikey never had the pressure to contribute to his family in the same way his brothers did.
"In 'Donnie's Gifts', Donnie makes an inflatable suit for Mikey so that he won’t hurt himself jumping around. This is a gift that noticeably annoys Mikey, as it gets in the way of his fighting style, which is very hyperactive and flashy. More specifically, however, he's upset by the prospect of Donnie feeling the need to baby him. (…) He doesn’t like being held back because his brothers are too concerned with his safety. It may be why he goes for such a— as he puts it— "razzmatazz" approach to fighting. He wants to prove he can do things without the intervention and supervision of his brothers.
"Raph is significantly more overprotective of Mikey than he is over his other brothers. This is a dynamic that seems to have a lot more depth than we are shown within the series and the only time it gets much focus is in the episode 'Hot Soup: The Game'. In this episode, Mikey decides that he is going to go on his first solo mission in order to retrieve a Lou Jitsu game from an auction house. Raph is the only one of his brothers that seems concerned at the idea of this. His concern greatly annoys Mikey throughout the entire episode, leading to Mikey making a few passive aggressive remarks towards his older brother.
"During Mikey's mission, he continues to bring up needing to succeed in order to prove to Raph that he is capable of doing things on his own. This desire to stick it to Raph isn't new either. There are quite a few small moments in the series that depict this slight tension in their relationship as far back as the first episode, where Mikey steps forward after Raph's failed attempt at opening the hidden mystic doorway and takes pride in managing to succeed where Raph didn’t. (Important side note: there aren't malicious undertones in this behavior, it's simply a petty 'gotcha' for Mikey to say 'See, I can hold my own just fine. I don't need you all the time.')
(…)
"I could probably go on and on about the little examples of this sprinkled throughout the show, but I think that would be redundant. Through all of this, it is easy to tell that Mikey hates being babied and treated as if he is incapable solely because he is the youngest in the family. He wants to feel as useful as his brothers and be able to protect them and be there for them in the same way that they are for him. As many youngest siblings do, this makes them desperate to be seen as an individual. He becomes more ostentatious with his self-proclaimed "razzmatazz" to draw more attention to himself in fights in a subtle act of rebellion against his brothers' overprotective attitude towards him. Especially towards Raph. Mikey actually appears to distance himself from Raph the most due to him feeling as though he needs to prove himself as independent to negate his overprotectiveness, whereas you will see him regularly clinging to Leo or Donnie for emotional support."
— "Mikey's Family Role"
by Skulltrot, discussing Mikey's character in Rise of the Teenage Mutant Ninja Turtles
by Skulltrot, discussing Mikey's character in Rise of the Teenage Mutant Ninja Turtles