My 5 months old keep on sucking his thumb when he is hungry or to smooth himself to sleep. I am worried if this become a hard ot quit habit. Will it go away when he is older?

No, you don't have to stop your child from sucking her thumb while he/she is still a baby. Babies generally suck their thumb to soothe themselves, which is good, because they need to learn how to rely on their own resources. The ability to regulate or control one's behavior and emotions is an important developmental challenge. Restricting them will interrupt their development. You can read up book by dr sear which he did mention it is normal for kid under two to suck thumb to self smooth themselves. I let both my girls sick their thumb and they outgrown it themselves without any need to introduce dummy or pacifier.

It is difficult to prevent him from sucking his thumb/fingers. Many ppl ask me to stop my boy from putting it into his mouth but i cant stop him.. so i let him be. I offered him a teether when he is awake to play with. By 5 months old, i'm already offering him a bolster/bean bag to hug it to sleep. Slowly, he no longers need to suck his thumb to sleep. He will hug his bolster and fiddle with a part of it till he fell asleep while I pat him. Now, he smells it instead to make himself slp while I still pat him. It makes him feels calm and he sleeps like tiz till now.

you have to cut the habit now. Soothe himself to sleep it's bascially treating it as a pacifer. If u don't stop now, it will be harder to stop as he gets older.

yes it will eventually go away. offer him something else, either a teether, pacifier.