How long would it take for me to get big biceps?

First of all, you suck at asking questions.

How heavy are you? How tall are you? What can you lift now? How big are big biceps?

If you are the average weight for a fourteen year-old boy 110 - 120 pounds and the average height 5'3'' - 5'5'' and you can lift a young beginner's weight - 5kg.

Let's say you want to be able to dumbbell take 15kg which is a lot for somebody your age.

Start off with 5kg and continue lifting everyday, one set is twelve reps so you should be aiming for 8 sets a day 2 at a time. Increase the number of sets you do and after a month you should be ready to move up to 8kg. Keep doing this until you are completely comfortable with 8 sets. Don't move up a weight class, 3kg, until you can comfortably do 8 sets of the new weight class.

It should take you nearly 8 months to move up to 15kg. You cannot rush this as building up your weight and muscle mass can take a lot of time.

If you are big boned it will be easier for you to build up your muscle mass. If you are not it will take longer but you can buy protein drinks to help bulk up and shave a few months off of training.