Actually, Dean does strike me as considerably more mature than Sheppard. He cracks wise a lot and takes a lot of pleasure in pop culture (a trait that reads as young even if lots of older people do the same), but he doesn't seem as inherently childish.

it's not so much the eye-rolling as it is the giggling and squealing.

Luckily I've been spared those fics to date.

he doesn't seem as inherently childish.

I admit I could have been paying more attention to SGA, but Sheppard only strikes me as young in the same way as Dean, or maybe Colonel O'Neill. As in, not when the pedal hits the metal. Just hoyish. Not particularly immature.

It's probably entirely sexist of me, but it makes me shudder whenever men in fic are described as giggling.

Drunk, stoned, or startled, they can giggle. Otherwise? NSM.

Childish: Tony DiNozzo. The SG guys, not as much.

My God Mrs. Ackles is fit.

Mr. Ackles is no slouch, either. He looks so adorable when he's not!Dean.

Drunk, stoned, or startled, they can giggle.

Yeah, I'll give you that. Although I might limit it to the first two.

Yeah, I've gotten to the point where all the constant eyerolling in fic is bothering me, as blue collar guys don't often show exasperation that way in my experience, in contrast to sarcastic teens and women with humanities degrees.

Sam's an eyeroller. Dean, not so much. He does more of the raised brow are-you-kidding-me face.

I've also read a lot of "he made a gagging noise" as either brother mocks the other, which always sends me to that scene in The Goonies with Chunk telling his story about the movie theatre. Needless to say, it pulls me right out of the story.

SGA's Sheppard canonically does a fair bit of young-seeming things. There are scenes of him playing with toy cars, debating Bat villains, pushing coworkers off of balconies, etc. His quarters were furnished in minimalist college student: musician poster, guitar, novel. I can see where the 13-year-old in a 40-something body fanon comes from.

Dean, not so much. While he likes his pop culture riffs, he seems to unwind by drinking, watching medical soaps, and getting laid, not setting up an RC car obstacle course with Sam.

Both men have dangerous full-time+ jobs that require adult concentration and judgment. But on the off hours, their attitudes seem pretty different.

Dean does actually claim to be Batman. I don't think calling him a teenager in an adult body is at all far-fetched. He may be post-pubescent (cf: porn consumption, masturbation), but still pretty boyish in his downtime.

Or maybe I'm judging adult male pastimes like prank wars and stuffing your face with food as being boyish.

Although I might limit it to the first two.

Startled!Sam giggling makes me want to giggle. I'm totally pro it. Dean, not as much.