How could Thanos have the Infinity Gauntlet at the end of Age of Ultron?

Question

At the end (post-credit) of Avengers: Age of Ultron, Thanos is seen taking the Infinity Gauntlet.

But in Avengers: Infinity War, judging from Eitri's words, his attack on Nidavellir, where he obtained the gauntlet, took place in a small time interval just before the events of Infinity War. There was Thor: Ragnarok between Age of Ultron and Infinity War and Nidavellir was unprotected after Asgard was destroyed in Ragnarok. So, it appears that Thanos attacked Nedavellir after Ragnarok.

So how could Thanos have the Infinity Gauntlet at the end of Avengers: Age of Ultron, given the fact that he attacked the dwarves and made them create the gauntlet just before the events of Avengers: Infinity War?

Answer 1

From my own previous answer:

Thanos decides to do it himself after (it is assumed) the events of Age of Ulton although it's not clear when this event actually takes place in the MCU timeline

We do know that Thanos had the Infinity Gauntlet constructed by Eitri at Nedavellir but it's possible that this actually took place considerably after AoU and we are just seeing the outcome as a flash forward and Thanos really started getting serious about the Infinity Stones just before IW after Odin has moved on from Asgard and Nedavellir was left undefended.*

Updated: Per this answer on SF&F

Per the film's Directors/Screenwriters Commentary, Thanos' motivation for deciding to gather the stones is that he finally (after many years of searching) learned the location of the lost Soul Stone. Before this he seems content to get on with obliterating one planet at a time and making sure that he knows roughly where the other stones are, safe in the knowledge that he's made himself powerful enough (through his armies and his 'children of Thanos') to go and collect them when the need arises.

Stephen McFeely: "The catalyst for the whole movie was when Thanos figured out where the Soul Stone was because he captured Nebula on his ship and rooted around in her brain and figured out that Gamora knew where the Soul Stone was."

Joseph Russo: "It's the reason why he hasn't gone for it before, because he knows that the minute he does, the forces of the universe are gonna line up against him. If he doesn't know where the Soul Stone is, then what's the point?"

^Source

^{* and Asgard is, as we now know, destroyed in Thor Ragnarok}

Essentially, it seems Nedavellir was destroyed after Thor: Ragnarok, and so Thanos could not have had the Gauntlet at the actual time setting of Age of Ultron so the post-credit scene in AoU MUST have been a flash forward.

Answer 2

This has been asked with screenwriter and director too and their answer from businessinsider

How does "Avengers: Infinity War" fit with "Age of Ultron"? Asked about this at a press junket, screenwriters Stephen McFeely and Christopher Markus seemed unconcerned about this. "Not our movie," McFeely joked. "We've all sat there and went, 'What the hell is he talking about,'" Markus added, "Where was he when he did that?"

Fortunately, the Russos themselves have an explanation. In an interview with Comic Book, Joe Russo suggested this scene is actually on Nidavellir.

"I think that it would be connected to Eitri," he explained. "I think that clearly he is the one who forged the gauntlet and Thanos had the gauntlet at that point in time. It's been a while since any of the Asgardians have interacted with Eitri and his people." The explanation makes sense; Loki took over Asgard at the end of Thor: The Dark World, and under his rule the Asgardians stopped protecting the other Realms. Thanos clearly took advantage of this.

So Thanos just took profit of lack of Asgardian's attention.