During my sex for the first time i just couldnt cum was that normal for a guy?

Yes, it is absolutely normal. It is all about stress.

This does happen to men of all ages sometimes. Stress is probably #1, but other factors could be alcohol or other substance use, also some prescription meds.
This happens to women also, even those that are quite orgasmic, some days its just not going to happen.
As long as your experiences are enjoyable and you DO ejaculate with self stimulation, there's probably not a medical problem.