Actually I tink most guys when doing it for the first time,
especially with a gf for the first time (even you had other girls
b4), sometimes will have higher chance of not able to come at all
then coming too fast. haha. But if you are the latter one, still,
it's normal to come fast due to over-excitement. But after a few
times when the two of you are more used to one another, experience
will improve so will the duration, style and "patterns",
hahaha.