Hi There,
The resolution for this problem is easy. The reason you are facing this problem is that "Store" thinks that you are a Child and they wouldn't allow you to download any application
Please follow the steps below:
1. On your phone, please go to Settings > Email + Accounts. In the list look for the first email marked as "Microsoft Account".
2. From your phone, use credentials of "Microsoft Account" to sign in to account.live.com.
3. After logining in to account.live.com, make sure that birth date and home country/region are completely filled-in and saved.
4. If you see a message indicating that your password is weak or something, please change to password.
5. If you are prompted to add additional security information, please do so.
6. From your phone, sign in to Xbox.com using same credentials above.
7. You "SHOULD" be prompted to accept terms of use. Please do so.
8. Click on My account.
9. Scroll down the page till you see Billing Contact Information. Click on it.
10. Make sure that information is up to date.
11. Power down your phone and wait for 30 sec.
12. Power on and try accessing Store and downloading apps.
Thanks,