Instagram b'day option

[D3F]

Registered on Instagram. Set all the parameters in the profile (Name, email & etc), but the birthday can't set. What could be wrong?
On web profile, there is generally no such options as a birthday.

 

[nydtech123]

there must be a b'day option....look at your profile page

 

[D3F]

In the web profile there are no such options like "Birthday" (only Name, email, Username, Phone N., Sex, Bio & Website).
If you go to your profile via mobile phone then there is "Birthday" field, but when you try to change it still does not change.