It was about 11 years, I think I started playing ADOM in the early 2000's, and my first win was in 2013.
I have to agree with the expansiveness of the game which surprised me. In some cases I wish I didn't spoil myself and found things on my own (HMV, temples, etc) - In some senses I didn't have enough time to figure all that stuff on my own because I was playing so many other games as a teen.
Beating the game in one month would be like studying for a huge final exam and acing it in the end!
Gate Closers:
Dwarf Monk (p17), Dwarf Paladin (p23), Gnome Duelist (r49), Dark Elf Barbarian (r50), High Elf Archer (r51)