The original trilogy of Star Wars movies was released before the PG-13 rating was introduced in 1984, one year after the release of Star Wars: Return of the Jedi.
This will be the second Star Wars spin-off to hit theaters, and the 5th Star Wars movie to receive a PG-13 rating.
This is understandable, as it is the same rating and reasoning that the previous Star Wars movies received since Disney first bought Lucasfilm and put out Star Wars: The Force Awakens.
The rating for Solo: A Star Wars Story describes the spin-off as having “Sequences of Sci-Fi Action / Violence.”