[FelixFelicis]

Okay, I get it, but by this logic you would also say that a 20-year-old is in his teens or a 50-year-old is in his forties. Base-10 system and all, we just don’t do it. IMO, this is a case where the intuitive, practical understanding of the general public has got to trump the esoteric mathematical correctness of a few ultra-literal snobs.

[La Enchiladita]

a few ultra-literal snobs.

Oh gosh, I am so busted:^)

[dr_lew]

Okay, I get it, but by this logic you would also say that a 20-year-old is in his teens or a 50-year-old is in his forties.

No, it's the opposite. Your first year would be Year One, and when you turned 1, your first year would be over, and you would be in Year Two, and so on.

When you turned 49, you would be in Year Fifty, and you would say, "I'm in my fiftieth year," instead of saying, "I'm 49".