How Long Does It Take to Fix a Medium-sized Teeth Gap?

Regular braces and Invisalign can work equally well for correction of space between front teeth. In most cases the length of time for such correction is the same whether braces or Invisalign aligners are used. Closing just the gap could take as little as six to eight months. But when there is a gap like the one you show, there are usually other associated bite problems that should be fixed at the same time. if so, the treatment could take longer. With an quick examination your orthodonitst should be able to give you a reasonably accurate estimate of how long your treatment will take.

With wires, it might be a bit faster, perhaps 6 months (if we are only talking about the gap). Invisalign will be around the same. At your age, comprehensive orthodontics would be best, as fine tuning the bite can be managed as well as facial development.
I would suggest a complete evaluation with a local dentist or orthodontist to find out a more clear estimate.