Better stick to prepaid because you have freedom.
Reasons not to subscribe for postpaid:
1.) 24 months contract
2.) monthly payment
3.) locked device
4.) service is not good(in terms of internet connection)
5.) super expensive
If you want to take the risk then its all up to you.
Pwede mag-apply basta may parent consent letter ka.
Strictly speaking you have to be 18 to be able to apply but I know of some who were allowed to some months before becoming 18.
You can try but so as not to waste your time I would suggest that you get a present Globe subscriber of good standing to act as your guarantor for liabilities you may incur until the time you turn 18. You may or may not use that depending on the credit investigator who would look at your application.