Don't waste your time...
A PSN Account's DOB cannot be changed..
All these Services offered by Sony have Terms of Service attached to them... You can change the Date at MobileSony but each element of the Sony Service have their own Terms of Service.
I've tested this DOB fully concerning the PSN Account.. it's unchanged.
If you select DOB for the Verification factor, it will only work with the original date used.
The only benefit of MobileSony is to check for the DOB used..
And this is a recent addition as many of the Privacy Laws have been changing recently.
DOB was a hidden feature before and the only other way to check the DOB was through a Game called 'GT Sport' where during signing up to online play, the DOB was visible.
Ava