I'm clear about using one hyphen while typing a sentence.
I met a 24-year-old girl. She was pretty.
But in many sentences I observe a longer dash (--). Probably they are two in number. Microsoft Word automatically does this at times.
In typing, is there any rule of putting more than one dash (-) other than describing two words as adjectives (as in above-mentioned case)?
Is it just a typing style or has to do anything with grammar?