You can deffinately do it! Consistency will help you get your strength back.
Hello ! Don't worry, you will get back at your former level in no time. And as the other members said before, being a good rider is not about your age or the number of years riding, but about your will to progress, your capacity to listen to your coach and to others, and your ability to adapt. The most important is to find a stable where you will feel comfortable and where you will be able to have fun while getting better.
Of course! I'm 23 and I took off 5 years from ages 17-22. It will take work to build up muscle and skill again but you can totally do it!
Of course you can still be a good rider! Horse riding can be picked up at any age. It's not about age, or even the number of years riding. It's about the quality of training and experience within those years. At 16, the only thing you're missing out on is riding Shetlands and whilst they're super fun, it's not the end of the world.