The youngest species on Earth is a type of bacteria that can eat nylon and are considered potentially only decades old or years old.
And some plants such as certain monkey flowers or a type of cress, have also been identified as new species which have evolved very recently.
Although we can only observe speciation events which have occurred within our own timeframe, so we might not be aware of very recent speciation events which are still unfolding.
Speciation is a gradual process, and it can also be challenging to determine exactly when a new species becomes distinct.
So it's difficult to actually poinpoint the absolute youngest species on Earth with great certainty, because the speciation is an ongoing process and new species are also constantly emerging.
Although certain bacteria, plants and insects are examples of some recently evolved or newly identified.
Some bacteria which have adapted to unusual environments like industrial waste or insects which have diverged into new species due to habitat changes, are also relatively young.
So in reality there's really no youngest species on Earth as everything is actually the same evolutionary age and likely also shares a single common ancestor.