The match was their final warm-up fixture ahead of the Jason Leonard Under 20 County Championship starting on February 11.
Devon had opened their season with a 21-5 victory over Gloucestershire the previous week at North Tawton.
The two games have allowed the county to have a look at a host of players ahead of taking on Somerset in their opening group match a week on Sunday.
“I was really proud,” said Paterson, who plays for Ivybridge, after Sunday’s performance. “It was a trial match and I think we have prepared really well for the County Championship over the past two games. We had a good win against Gloucestershire and a tough game against Cornwall.
“Cornwall are very strong in terms of their set-up and it can only make us better for the championship, which is the main thing. Obviously, it was disappointing to lose because of the Devon-Cornwall rivalry, but we learnt so much.
“The players have got good exposure and great competition. By playing Cornwall and Gloucestershire we have played good sides and it has given us a really good eye-opener to the abilities we are working with.”
He added: “Everyone got some game-time against Cornwall, which was positive.”
Devon started well on Sunday, but it was Cornwall who took the lead on 17 minutes when flanker Jack Osborne scored from close range after pressure from a scrum. Reuben Edwards converted to put the Duchy 7-0 up.
But Devon hit back thanks to some impressive scrum work. They pushed Cornwall off their own put-in on their own line to earn themselves a five-metre scrum. From it they got the push on and Torquay number eight Josh Mackin was there to score.
Mackin had also managed to cross the whitewash against Gloucestershire and made some powerful runs on Sunday.
Just before half-time, Cornwall scored a second converted try when Chae Jenkins went over on the right. That put the visitors 14-5 up at the break.
Devon cut the gap to four points nine minutes after the interval when Callum Smith got the ball down from another good scrum. The game lost its way a bit after that with both sides making plenty of changes, but Cornwall managed two more courtesy of Jack Hodge and Will Gibson.
Devon under-20 squad that faced Cornwall: Dan Armstrong (Exmouth), Kyle Blackmore (Honiton), Dino Bozic (Exeter College), Ben Collins (Ivybridge), Josh Davey (Crediton), Bradley Down (Hartpury College), Sam Fulthorpe (Exmouth), Owen Garner (Ivybridge), Tom Gosling (Brixham), James Goss (Exmouth), Robbie Guthrie (Crediton), Joe Harris (Exmouth), Jamie Hulland (South Molton), Aiden Humpries (South Molton), Tommy Jermyn (Crediton), Dan Johnson (South Molton), Ethan Justice (Exmouth), Harry Jones (Bideford), Maximilian Keen (Exeter College), Ryan Lee (Barnstaple), Robin Luscombe (Ivybridge), Josh Mackin (Torquay), Ned Millsey (Exmouth), Adam Northcott (Ivybridge), Harry Ottaway (Exmouth), Alfie Pennyfield (Barnstaple), Mitch Pinkus (Ivybridge), Marcus Prout (Ivybridge), Lewi Riley (Ivybridge), Callum Smith (Brixham), Lewis Swatton (Tamar Saracens), Jay Toogood (Ivybridge), Wes Vermigle (Ivybridge), Adam Walker (Ivybridge), Morgan White (Exmouth), Troy Willis (Barnstaple).