According to the given information, the mean age of 25 people in the cinema is 24, which means the total age of all 25 people is:
25 people * 24 years = 600 years
When the new person arrives, the total age becomes:
26 people * 25 years = 650 years
The difference between the two totals is the age of the new person:
650 years - 600 years = 50 years
Therefore, the age of the new person is 50 years old.