Draco as a Death Eater.

I was rewatching HBP the other day and the thought struck me- why did all the others in the order automatically assume that Draco could not be a DE because of his age, when they all knew full well that Regulus joined at the age of 16- surely Sirius must have told the rest of the order that. If Regulus had done it, what made it so impossible that Draco would?

I dunno. Maybe there's an answer and I'm just missing it.

I'd thought about that before too, about why his age should be such a deciding factor to them that he simply couldn't be a Death Eater. I haven't been able to think up any really excellent reasons yet, but the best I've got is just the fact that they underestimated him. If you think about it, why would the Dark Lord choose a sixteen year old when he has so many others around to use? Why would he pick Draco Malfoy, who had never really presented himself as much of a threat before (other than taunting Harry on occasion and picking on Mudbloods)? They had seen no indication that Draco would be any kind of formidable ally for Voldemort, even though his father is a Death Eater.
Regulus was more obviously obsessed with the idea of Lord Voldemort and the Death Eaters, as he had all the newspaper clippings and stuff saved up in his room. Draco didn't. He was just a Slytherin, just a sixteen year old student who had shown no obvious interest in Death Eaters other than being a son of one, and the Order did not feel threatened by him and didn't see any reason that he should be a Death Eater. Since no one saw him excited about Voldemort's return and being a Death Eater and whatever else, no one believed he would be dedicated enough to go through with it, and no one believed Voldemort would accept the kid as a servant.

I agree with almost all of that, but I don't think it's true that Draco showed no interest- as he grew older, I think he distanced himself more from it, not wanting to make the same mistake as his father and flaunting his allegiance, but he has made clear on numerous occasions that he supported the Dark Lord's values and regime. Still- I agree that it would not warrant enough attention from them to actually believe Draco would join, and I don't think the thought even struck him that Draco would have virtually no choice about it all; the very idea that Voldemort would punish the Malfoys by taking their son was unlikely to be considered at all.

Exactly. The thought just seemed too farfetched to them that Draco should be made a Death Eater. What use was a kid like Draco to the Dark Lord? They couldn't have known Voldemort's intentions for the boy, that it was to punish the Malfoys, or that it was forced rather than voluntary. They were only looking at it as Draco wanting to join, and they couldn't see enough evidence for that to be true. They didn't see his interest and they didn't think the Dark Lord would accept him, so it only felt logical that Draco Malfoy could not be a Death Eater.

Poor Draco.
My heart honestly breaks for him.
I'm too attached, perhaps.

Also probably a negating factor was that Draco was accused by Harry. As his school time nemesis they all think that Harry over-reacts to Draco in every way so this seems even more far-fetched because of that. Also Sirius was already separated from his family when Regulus joined up and it might be that during his first rise to power Voldemort was behaving differently, recruiting in the school and whatnot. There is no evidence of this in his second rise so they probably also took that into account.