I think I see what he's saying but it's half wrong, half right.
Technically, if you were born on, let's say Jan 1, 2000, at thst point, you're 0 years old.
On Jan 1, 2001, you are 1 year old.
So it shouldn't be a single point, but a slope.
Because the date has changed by 1 year, but you have aged by one year.
Otherwise, this chart does show, like he said, that on one date, you have been 70, 45, 10, 32, etc all on one date.
Now if the date excluding a year, just as only Jan 1. And there were 366 (including Feb 29) plot points, this graph still doesn't make sense.
Because it says you only have an age on your birthdays. So if your birthday is Jan 1, and you look at this chart for how old you will be on Jan 2... There is no point. You don't have an age.