The Welsh striker is having his first experience at U21 level this season.
Lewtas told liverpoolfc.com: "Lewis has been brilliant for us, he really has. He is a real energetic frontline player, loves to run in behind, he is aggressive in how he approaches the game and has really good technique. He is a really good footballer.
"He has fitted in great with the lads, he has a fantastic character and he just gets on with it, he really does. The other day when we were talking about Lewis, you forget he is still an U18 player. He has really matured the way he plays.
"Against Barrow, playing against a senior backline, I thought he was great for us and for them he was an absolute nuisance, the way he played and approached the game. I'm really pleased for Lewis. He has shown good versatility playing across the frontline this season and he is a player who has made massive progress this year. In fairness, he has carried that on because I thought he was fantastic last season for the U18s."