I'm still sorting out what we really mean when we keep referring to the guy as "an uncle". Is he also a father? Is he married? What's the description of "uncle" adding or informing us of? My immediate reaction makes me think he's a 50yo with no kids, maybe a girlfriend, but his sister had kids. I don't know that this is an accurate perception or if it even aligns with how other people read it. Just seems kind of weird that he's summarized as this title.
"An uncle" is just a way to refer to someone mature, unrelated to family connections. Kind of like the popular "Uncle Roger" https://www.youtube.com/c/mrnigelng (usually I'd expect a "generic uncle" to have no family of his own)
