My coins are not staking in wallet and it says: "Not staking because you don't have mature coins"

What does it mean?

My coins have been staking without problems so far, although I've just received 1 transaction in the past. Today after I received my 2 mined transaction the coins are not staking anymore.

The 2nd mined transaction is saying "Immature, 20 conformations will be available after 90 mined"