What is the age to have a contract with tmobile?

It was my mom bday last Tuesday and my aunt sent her a iPhone 5s from T-mobile and she say it was unlock but is not. So she said I can have it since I have a iPhone 4 so what is the age to have a contract with tmobile and do I just pay the month and how much thank you

I don't understand, please edit your question to make more sense.

Tmobile does no longer have any contracts. All their plans are month to month.

$50 a month = unlimited talk and text with 500MB of data internet
$60 a month = unlimited talk and text with 2.5GB of data internet
$70 a month = unlimited talk and text with unlimited data internet

So you can activate your own account with one of these plan on a individual account.