it would be concerning if a cause is not apparent. dry air colds sinus infection nose-picking trauma all can cause nose bleeding. it would be concerning if this happens frequently or if he is having bruising in other parts of his body without apparent trauma. nose bleeds need to be stopped properly and many people do not do it correctly. use your search engine for nosebleed or epistaxis management on webmd and you will find the right way.
should i be worried about my20 year old sons nosebleed that took so long to stop? . he must have bled for a good 30 minutes. it wasn't until he pulled what looked like a huge blood clot from his nose that it stopped bleeding. it looked like a big slug.