It may not ever stop. Seriously. But it will change over time. At some point (probably before age 3) he will stop swallowing things, and just mouth them. Some kids are more orally (I hate to use the word 'fixated') inclined than others. My son gave up his paci on his own at 6 months, but put all sorts of things in his mouth. He didn't swallow much, but he mouthed a LOT. And when he was older in K and 1st grade, he chewed the collars of his shirts. And when he was older (2-4th grade?) he chewed his pencils and erasers. Now that he is in middle school, he just makes weird noises with his mouth/throat when he is concentrating, lol.
I remember doing things like that myself, maybe you do too? I didn't chew my pencils, but I sucked on the front collar of my shirts and even my HAIR (I had long hair). So, don't worry about there being a problem with him, just worry that you'll miss something dangerous... Sorry... that sounds more scary than it should. ;)