It's a little subjective. If you don't do any map completion, jumping puzzles, or events and just move from story mission to story mission, you can do it in a few days. Hardcore speed runners can probably do it in less. Story chapters unlock every 10 character levels, ensuring you're at max level when you get to the end of the core game.

There aren't many achievements tied to the core game story. Most of the PvE achievements are related to things in the open world until expansions where achievements also exist in story instances. I've played since beta and haven't completed all of them. Achievements like "Shield Master" just take so much time, because you have to get 5,000 killing blows with a shield.

I hope this is informative.

"All PvE achievements" is a huge undertaking, even if you're just talking about the core game; there are things in there like Fractal God, which will take probably a year or so of dedicated grinding, and God Walking Amongst Mere Mortals, which will require finishing a huge number of achievements in a totally different game. I've been playing since a year after launch, and I'm nowhere close to having all the core achievements.

12 years and counting for me

As people have been saying, the real gotcha here is the all achievements part. achievements in gw2 are an essentially endless task and activity to go for. I don't think anyone in the entire game has all of them.

I haven’t played in a few years, but when I 100%’d on my second character it took me a year or so of daily play. I can’t be sure of total hours spent, but it wasn’t insignificant.

Totally doable though!

Ignoring the all achievements part, story and world exploration could be finished in a week or in like 6 months. Honestly my suggestion would be to not rush it as it defeats the purpose