Birthday is correct, age is wrong.

[ogoalex57]

I put my birthday correctly, but the very next page says "since you're 23", but i'm 24 as of like 2 months ago rofl

[Melaine]

Remember, your age will be based on the age you were in 2016, for your 2016 taxes.

[amax125]

That may be true, but the sentence is still wrong.  By the way that the sentence is structured, it is telling you your age in the present tense.  It should read "Since you were 23 on Dec. 31st, <year>, ...".