Amavi lost possession in the 87th minute at Selhurst Park, allowing Palace debutant Bakary Sako to secure all three points for the hosts with a fine finish.
Earlier, Scott Dann's 71st-minute opener had been cancelled out as Villa new boy Adama Traore - making his debut - saw his cut back deflected into the net.
Asked about Amavi's error, Sherwood told reporters: "That's what you will get with young players, unfortunately.
"Jordan hasn't made many mistakes since he's been here. That's one and he will have to learn from it.
"We have a lot of good young players. We have added a lot of youth to the squad. Unfortunately you will get ups and downs with young players.
"I have been in that boat before, I have seen it. But I know how to develop them. He made the wrong choice. But you have to learn. He will - he's a good player."
Pressed on substitute forward Traore's impact, Sherwood added: "You saw a young player who has no fear at all in Traore. He burst forward and lit it up today in a short period.
"I thought it was the right time to put him on. That's what he is capable of. We know what he possesses. Hopefully those Villa fans can see a lot more of him.
"I will make sure he gets the right opportunities at the right times."