You wont be able to compete in the 2016 Olympics because you'll only be 17 and I'm sure you have to be 18 to be in them. As for the 2020 Olympics however who knows all I can say is keep training keep doing your best and who knows maybe you will be in the Olympics.
Yes you can even if TeamGB doesn't pick you for the Olympics.
There is the Independent Olympic Athletes which compete under the Iinternational Olympic Committee Flag (5 rings, headquarters in Switzerland) however with this you're purely self-funded i.e. you pay for your own training (if you're picked for TeamGB then TeamGB pays for your training and uniform), you pay for your own uniform walk into a shop and purchase the kit, all white, you pay for your own accomodation, flights and food (which the Olympic Committee pay for). This option is used for teams who have fallen out with their Olympic Committee, countries which do not have a Olympic committee, athletes in political transition etc. you apply direct to the Internation Olympic Committee in Switzerland.
It is certainly possible. you have good ability and as you grow and gain experience you will compete against better athletes.
You will still be very young in 2020, so continue to do what you enjoy, and we might see you in the games.
I'm 13 years old and female, started training in tae kwon do last year and am now doing tkd 3/4 times a week. I've won gold in all five sparring competitions I've participated in (incl. British, English and Welsh)and may be looking into starting kickboxing. Could I make it? Either in 2016 or 2020.
