I can't remember the first time I received a BJ. But it was not until I was 30 that I blew my load during a BJ. Up to that point, a BJ was always just part of the process, never the main event.
The first time I shot my load was with a neighbour that I had been up fixing her plumbing for. She was a single mother and would sometimes invite me up for dinner in exchange for helping out around her place. One afternoon she offered the BJ.
I remember sitting on the couch, leaning back while she kissed me and pulled my pants down. She was giving a really good hand/mouth bj when I mentioned that I had never cum from oral. She stop with the bj, keep with the hj and told me that she would show me what I was missing. She immediately switched into PSE and deep throat and worked me until I shot down her throat and she swallowed.
Later, she told me that she had been a call girl, and at the time I had to ask what she meant by that. Oh, how times have changed.