I'm 30 but I'm obsessed with a 16 year old girl
Why are you obsessed with someone so young?
I am not sure, I cannot help it.
You should not be obsessed with someone so young. Do not act on it as you will end up in jail.
It's fine, I hide it. She doesn't mind the attention.
You need to stop interacting with her at all. It is wrong to do so and you will be charged with grooming her. Be interested in someone who is an adult at least.