I am thirty years old.
'Trent'anni' = tren-TAN-nee — the elision of 'trenta anni' to 'trent'anni' is standard. The double 'n' is held slightly.
State your age when asked, or volunteer it early in an introduction if relevant. Age helps calibrate social register (tu vs. Lei) and shared generational references.
Italian uses 'avere' (to have) for age, not 'essere' (to be). 'Ho trent'anni' = 'I have thirty years.' The elision 'trent'anni' occurs because 'trenta' ends in a vowel and 'anni' begins with one. This pattern repeats with other tens.
Ho ventotto anni.
I am twenty-eight years old.
Numbers above twenty combine with a vowel elision: venti + otto → ventotto.
Ho quasi quarant'anni.
I am almost forty years old.
'Quasi' (almost) softens the number — common in casual speech.
Compio trent'anni a marzo.
I turn thirty in March.
'Compire gli anni' = to turn a specific age — adds detail about the upcoming birthday.
Complimenting someone on looking younger than their age ('sembri più giovane') is universally well-received in Italy and considered a social grace rather than a hollow flattery.