You get the Yearling badge in proportion to the necessary reputation and the age of the account. 200 reputation in one year is sufficient for the base point, but if you miss that requirement, then you don't automatically get the badge when you hit 200 reputation. Instead, you have a higher threshold to reach based on your current age. If, for example, you are at 1.5 years, you require
1.5 * 200 = 300 reputation to get your first Yearling badge.
On August 16th, fivetwentisix ended up at 495 reputation after earning 23 over the course of the day. At 2 years and 5 months, he would need at least around 483 reputation (plus or minus a bit, no more than 11 as it were) to qualify for getting the badge. In this scenario, because it's been over two years, he then earns the Yearling badge for both years in question, for finally reaching that rate of required yearly reputation. Assumedly, prior to this, the user had always been underneath the required threshold to even earn the first badge, for over a year as it were.