Just as people have different lengths they also have different heart rates.
With 90-100, you are in the category of people who have a "above average" but acceptable heart rate.
What causes this heart rate is not to say other than that it is congenital.
If you are not really fit at the moment, you could probably get it a little bit lower with physical training.
I should add that I am...not exactly athletic but not out of shape. I'm 5'5" and weigh 125 pounds at most. I used to be more active when I was in school, but that seemed to have no effect on my heart rate. It does go up if I do exercise, but I have exercise induced asthma so I don't do much cardio.
I would not worry about it.
Your heart rate is not outside the "normal" range, it is like this for many years and it does not cause you problems, so its just fine.
I would eliminate possible causes before calling it normal. At the age of 16 your heart rate should have slowed down, to around 70. Your blood pressure is also a tad high at 120/80 for your age. Have you had any blood tests or EKGs to see if anything is going on? have you ever been to a cardiologist? I think it would be wise to make sure everything is ok before labeling it as ok. When you take your pulse how are you doing it? are you making sure you are seated and fully relaxed? or are you anxious it might be high?
Blood tests and EKGs are scheduled, yes. Have had blood tests in the past that showed nothing. When I take my pulse after sitting/laying for a while it's usually around 92 or so. Although right now as I lay here it's 84. Low for me.
I could be a bit off on my blood pressure...most recently it was 101/76. It may often be 120/70ish rather than 80.
And my anxiety is pretty bad. It can manifest itself physically in other ways (headaches, stomach aches, etc.) so I wouldn't be surprised if when they take my blood pressure it goes up a bit just because they're taking it.
Please let us know what your blood tests and EKGs reveal :)