ENT examination is first thing that needs to be done followed by Audiometry. What type of hearing loss is existing needs to be seen Putting sand in the ear per se does not cause hearing loss Attempt to remove the sand by unskilled doctor might cause damage to the ear drum or hearing loss Are there other Co existing complaints like tinnitus or ringing sound in the ear? Any discharge or vertigo?

Putting sand might not be the cause of his hearing loss. He needs a detailed evaluation. It is possibly a nerve damage due to some cause. So there is a possibility that it can get worse with age. A definite answer can be given only after detailed evaluation including audiogram

Hi , you need to do a audiogram first to see what type of hearing loss he has , and that will predict whether the hearing will deteriorate or not. History of other symptoms such as ear discharge , giddiness are important  which will indicate to primary cause of hearing loss..