Why can't a second user, not an administrator, activate ths mobile data on my Samsung Galaxy s4?

[Android Central Question]

I set up my account first, then my partner did, but he's just realised he can't turn on the mobile data. He's not using a restricted account, but I also can't add him as a second amdinistrator.

I feel like we're missing something, but if not this is a big let down on basic functionality that wasn't obvious when we first set up the tablet.