u mean the first movie? I think she was around... 5-6? I have read somewhere that Simba spent about 5 years away from Pride Rock (because it takes 5 years for a lion to develop a full mane). And i guess Simba wasnt even 1 jaar old when he went away, and Nala must be the same age as him. So 5 years of a little bit older, around 6, after all at the end they have a cub. Which means some time must have passed. Well, others can have different opinions though.