There are plenty of people out there like you....doings things unwise despite the number of people saying to do otherwise.....so I won't tell you what I think of a 16 year old making it with a 20 year old.
Does sex hurt for the first time? For some it does and for some it is just uncomfortable and for some it is pleasurable. I guess you will find out what it is for you.
If I tell my boyfriend to stop and he doesnt , what do I do? This is a question that, if you were an adult and mature, you would have answered for yourself, before you got into a sexual situation. This is a big red flag you aren't ready. The answer for you is that you DO NOT have sex with someone you don't COMPLETELY trust with your welfare and safety. By asking this question, you gave all of us the ammunition we needed to tell you what you don't want us to say.
Will I bleed? Some do and some don't....you will find out for yourself what is true for you.
I'm one of the top answers in this category with common sense wisdom. It will be your choice to listen or not. To me, you are like the person in the lake who is drowning but yelling....."Don't save me!"