The
2021 Matriculating Student Questionnaire, which is given annually to first-year med school students, reports the following:
31.4% of students had <1 year pass since college graduation
44.8% of students had 1-2 years pass since college graduation
15.2% of students had 3-4 years pass since college graduation
8.5% of students had 5+ years pass since college graduation
Not sure if anything has changed due to COVID, but you can see that the % of students with no gap year(s) has decreased from 2019 to 2020 to 2021.
If you're interested in looking at individual schools, you can take a look at the Age Ranges for the First Year class. However, age ranges are broken down into 19-23, 24-29, 30-39, and 40+, so there's no bracket for ONLY no gap year students. It could help give you an inkling of what individual schools are looking for. For example, one school that always stands out to me is UC Davis, which has >75% of their first-year class be 24+ with <10 students older than 30 years.