Assuming you were arrested by local police and not the ATF or FBI, You won't do any real time as a 16 year old. The law says you can, and in a worst case scenario you could, but anyone i know under 18 caught with a minimal amount of weed has never been in jail for more than  a week. Most get community service or probation or some other kind of deferred sentence. You won't be charged with a "federal crime", you will be charged according to the laws of the state. Which also means you WILL be charged as a minor, which is great. It means the courts will see you have no history and be very willing to let you basically get off with a slap on the wrist. And while it could come out if you run for president, juvenile court does a decent job keeping your record stashed away for future employers to never see.
Honestly you have more to worry about with the cost of a lawyer and court fees, and the wrath of your parents, than real jail time.