And the 20-year-old has no greater inspiration to look to at the Welsh region than fellow lock Jones, who at 29 is closing in on 100 caps for Wales.
Warren Gatland is also a big fan of Thornton after naming him in Wales' 47-man World Cup training squad, which he will join up with after the Under-20 Championship.
Thornton will skipper Wales Under-20s during the tournament - with France lying in wait first up on Tuesday - and Lewis believes the influence of Jones will help him shine throughout the tournament.
"He is impressive, not just as a player but as a person," said Lewis.
"He's sensible and he has made tremendous progress since coming through as an 18-year-old.
"The Ospreys are giving players like Rory the experience of playing in major games and that will only help his development.
"He also has a great role model in Alun Wyn Jones, an individual who is not just of the world's best locks but also a leader. He can pass those leadership skills on to Rory."
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