You are absolutely correct!Depends on the guy and how excited he gets. I had a 19 year old guy with a very nice cock. He wasn't very experienced and came almost as soon as I took him in my mouth. Fortunately being young it took him no time at all to get hard again and having got over his initial nerves and excitement was able to give me a very good fucking. So experience does count for a lot too. That said, some guys are always quick cummers. My first husband was a case in point - only ever lasted a couple of minutes on average - very disappointing.
But experience or inexperience is not a matter.
Preejaculation can be cured by treatment....