I don't try to last a long time when getting a bj. I think guys think they have to last forever with everything but really with a bj there is no point, not like you're gonna make her mouth cum. Now sex is a different matter, you have to be able to make her cum, but that is more about technique/size than anthing else. Also being able to turn her on before your clothes are off, but thats another thread altogether.
I dont mind giving head, actually with my last guy I actually got into it bigtime because I wanted to please him so much. I just wish that he wouldn't hold out for so long though LOL. He would keep holding out because as he put it, "He didn't want the feeling to end..." I was flattered by the fact that he enjoyed my skill, but after a while my jaw would start to hurt... heheheheee
If he hasn't came after 30 minutes of serious head bobbing action then you must be doing something wrong. Besides after 30 minutes my entire mouth, neck, and throat start hurting.