How do you say are nine years old in Gaelic?

There isn't one single Gaelic language. You need to specify which Gaelic you mean:

* Scottish Gaelic: Tha mi naoi bliadhna a dh'aois. (Tha mee noi blee-ah-nah ah dhee-ish)

* Irish Gaelic: Tá mé naoi mbliana d'aois. (Tah meh noy blee-ah-nah dee-ish)

Both translate to "I am nine years old," but the pronunciation differs.