I took one before I started kindergarten. Old IQ tests used to measure "mental age" and then they would use that to calculate the IQ, the old formula was mental age ÷ physical age × 100 = IQ, but that would result in inflated childhood scores, now modern IQ tests measure your performance compared to others of your same age in different areas, and then average the scores from the multiple areas to calculate a full-scale IQ. So if you do better on the test than say 99% of others of your same age when you are young, you'll probably do better than 99% of others of your same age on IQ tests when you are older.