First, what state are you in? That would help immensely.19 and 16 shouldn't be a problem legally. If it's within a certain number of years, it's not illegal. I had a girlfriend when I was 17, and she was 17, and she turned 18 first... by 3 1/2 months. It was not illegal during that short period of time.
I cannot date a 16 year old now. Thank goodness I'm starting to find them less and less attractive now. I guess I'm not the pedophile I feared I could become. I don't think I could spend more than 5 minutes in the same room as a 16 year old. My eardrums would explode.
The question I have is will you turn 20 before she turns 17? Then, you're starting to push things a bit.