If $100 from your father is net money that you can invest, then you can buy Bitcoin gradually every month. But if it has to interfere with your other finances, meaning you will have other needs that might use that money, then you have to manage your finances first. It is important to know the appropriate amount that you can invest gradually. Just be consistent, if your ability is $30, then do it regularly every month, and you will see that your Bitcoin accumulation is quite good in the future.