Yes it is good to start trading with a small amount, it helps you to put things into perspective and learn from it and even if you end up losing the money then you can be sure that the money that you are losing is not very much. Better to start with a small amount as a newbies, it is the smartest thing that you can do.
in fact $ 100 for a beginner to supplement an acceptable amount as a seed money. But if we talk about broader investments, then 100 dollars can be enough to buy only one specific coin, which can bring good profits. For example Ripple, which you can buy at 50 cents, and expect a price increase of up to $ 10.