Classmate in 7th grade while warming up for gym class stretched easily that way. One kid made the offhand comment “Hey, you can suck your own dick!” and flexible kid immediately yelled “SHUT UP!”. Which told us all he’d done it.
For the curious, I did know someone who said they could do it. We didn’t have long conversations about it or anything but he said all you need to know.
“It’s more like sucking dick than getting your dick sucked.”