I never actually got that far in the game. How long does it take to actually win the game? It looks like there are an insane number of levels, etc... to grind through?
It's been something like 7+ years since I've touched Nethack, but it still holds a special place in my heart. That being said, there's people that have been playing it for years and have not beaten it. When I played, I got super obsessed with it, I read the entire wiki front to back, had most facts of the game devoted to memory, and had beaten the game 3 times (with a 4th victory within spitting distance, but I choke to death on a Titan corpse literally feet away from the finish line thanks to a fateful misclick) and I have alot of stories that still rile me up to this day, if you can't tell!
There's the free version you can get from the Nethack website, there's the online version you can play in java that has worldwide leaderboards, there's texture packs if you don't like ASCII, and there's an graphically updated version available on Steam for a few bucks that uses isometric view but apparently has slightly reduced gameplay functionality.
So yeah, asking how long it will take you to beat it is a hard task, cause you can blitz through the game or you can take your time and farm every last enemy, the goal remains the same either way: Grab the amulet of Yendor and get out, ascend to the astral plain, and claim your ticket to demigodhood. There's 40-something floors to the dungeon if I'm remembering correctly, plus four elemental planes, plus the final astral plane, plus Sokoban, plus each class' unique Quest, plus the mining gnome village, plus some other secret optional stuff! There's actually so much to the game that even though I spent several months obsessed with it, I didn't get to see it all.
While the game is "Permadeath" which is the roguelike creed, you can copy and save your save files if you're a huge coward. I don't recommend it, as savoring the finality of death adds to the fun and the tension. You'll never get better at the game if you give yourself leeway like that, you have to trust in your ability, knowledge, ingenuity, and experience even when the game gets brutal. No matter how much you grind, no matter how powerful your character gets, there will always be things that can kill you, often instantly or nigh-instantly, and learning to deal with, prepare, avoid, and combat those things is what sets apart the dying characters from the winning characters.
I highly recommend the game to all experienced gamers, I'd put my victories in this game on my professional resume if employers would take it seriously, as the game is a test of personal mettle that most people simply can't handle, but I'd say everyone should seriously experience and attempt atleast once in their lives. It'll leave you with scars and memories you'll never forget.
And if everything is looking grim, just remember the magic word:
"Elbereth"
I'd buy a doormat that just had that word on it, it's the only thing I'm sure would keep monsters out of my home.