Kevin McCallister is 8 years old in the original Home Alone film.
This age is stated in the movie's script, plot summaries, and official sources tied to the 1990 release.

Age in Sequels

In Home Alone 2: Lost in New York (1992), Kevin is around 10 years old, as he tells hotel staff, though some discussions note timeline inconsistencies with the first film's events set about a year prior. Kevin's passport prop from the first movie suggests he was nearly 8 during its December events.

Actor's Age

Macaulay Culkin, who played Kevin, was about 9-10 during filming of the first movie, aligning closely with the character's age for authenticity.