Rule reminder
Ask age: 'Quanti anni hai?' (informal), 'Quanti anni ha?' (formal/3rd person). Answer: 'Ho [number] anni.' Age numbers contract before 'anni': vent' (20), trent' (30), quarant' (40), cinquant' (50), sessant' (60), settant' (70), ottant' (80), novant' (90).
Someone asks 'Quanti anni hai?' and you're 15. What do you say?