At BMI of 26 sounds good on paper even though the optimal BMI is between 19 and 25, but I'd still make sure that the fat:muscle ratio is also healthy. What is more important than BMI is waist to hip ratio and anything above 0.85 or a waist circumference of above 88 cm increases risk to develop disease
BMI is a cookie cutter measurement, it doesn't take into account how much of your weight is fat...so if you're exercising and eating healthy, don't worry. Still, it means you could stand to lose a little weight, and the sooner you do this, the better, it will be easier to lose weight while you are so young.
Yes a BMI of 26 can be healthy. It all depends on how you are in everything health-wise overall. BMI is only a tool that should be used in combination of a bunch of different things to assess overall health.
There are a lot of athletes who have unhealthy BMI, but are healthy. This is because BMI doesn't take into account muscle mass. So I wouldn't care only about BMI. I would get a physical done at your dr's office, they will run a bunch of tests to see how you are overall for health.