Date of Birth in Views: Age is 1 day ahead of desired value
The problem is that "Time ago" has no understanding of leap years so when it is calculating an interval it uses a "common year" which is 365 days.

If we go back 30 years ago from today (2018-11-08) to 1988-11-08 and then use a date time calculator we get 30 years exactly, OR 360 months, OR 10957 days.

If the "Time ago" was smart enough to subtract the years, following by the months, followed by the days then it would come up with 30 years, 0 months, and 0 days. The problem is that it does all of its math in days and then tries to convert to years.

10957/365 = 30.019 common years or 30 years and a week. This is because there was 7 leap years between 2018 and 1988...

So there isn't anything wrong per say. It is actually doing exactly what you asked it to do.

You can get much closer if you divide the date by 365.2425 which is the average length of the year of 365.25 which is defined as a Julian year. Julian years are used in astronomy.