Oh my! Can someone explain about splitting the number like this? How do you know it isn't eight teenage boys playing? How do we know that "déag" modifies "ocht" and not mbuachaill? Thank you!
Déag is a noun, not an adjective. “Eight teenage boys playing” would require the sentence to change to either Tá ocht mbuachaill ina ndéaga ag imirt or Tá ochtar buachaill ina ndéaga ag imirt. (I’m surprised that the original sentence didn’t use the personal number form.)
I don't think you use it for numbers above 12. At least, Gramadach na Gaeilge isn't showing it being used.
You’re absolutely right — 12 is the highest number with its own personal number form.
Can anyone explain why "mbuachaill" is singular when there are 18 of them?
For numbers, people use the genitive plural form. Most other nouns use the singular.
Bet you, if you tried today, you'd forgotten half of it. Have a lingot though ;-)
I once saw the 31st (as in the date) written as ' an t-aontú lá déag is fiche' (the eleventh day and twenty!) You'll also hear things like 'trí scór go leith' to mean seventy (three twenties and half a twenty!) You gotta love it.
If you are saying, the boys are playing [football], then the verb "ag imirt" makes sense. But if the boys are children and they are just playing - i.e. not playing a particular sport or cards - then the verb should be "ag súgradh".