Premature oxidation is like when you bake a cake and it turns out bad even though you followed the recipe. In the case of wine, it means that the wine starts to get old and bad before it is supposed to.
It's like when you buy a toy and it doesn't work right away, it stops working even though you didn't use it that much. Or if you make a drawing and it starts to fade and look old even though you just made it yesterday.
Wine needs time to age so it can taste good, just like when you cook your favorite meal and let it sit for a while for the flavors to mix together. But sometimes wine doesn't age right and it turns out bad because something went wrong. The wine may have had too much oxygen, which can make the wine taste old and bad. This can happen if the bottle isn't closed tight enough or if there's too much air in the bottle.
So, just like how you need to take care of your toys and drawings, wine needs to be handled and stored properly so it can age well and not turn bad before its time.