Young came off the bench to supply a nerveless finish in the 68th minute and secure the win after Daniel Agger had headed Denmark into an early lead only for Darren Bent to equalise almost immediately.
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The night was notable for two promising performances from young midfielders on opposite sides.
The 19-year-old Jack Wilshere put in an assured display in a deep midfield role for England, hinting of better things to come without really catching fire.
While Wilshere was assured, he was outshone by the 18-year-old Christian Eriksen, who came closest to a goal to crown an outstanding display when he slammed a shot off the foot of a post in the first half after good work by Nicklas Bendtner.
England, who face Wales in a Euro 2012 qualifier next month, made a ragged start and fell behind when Eriksen fired in a cross from the right and Agger flashed a glancing header past Joe Hart.
The Danes held the lead for just two minutes as England responded in style, with Theo Walcott robbing Simon Poulsen on the right and crossing to give Bent an easy finish.
In his first game as England captain, Frank Lampard had the ball in the net in the 41st minute, only to have the goal ruled out for offside.
England made three substitutions at the break and immediately got a grip on the Danes, dominating possession. The best of the chances fell to Bent, who forced Thomas Sorensen into a number of fine saves.
Dennis Rommedahl could have put Denmark back on top in the 64th minute but fired straight at the keeper after the lively Eriksen had set him up with a cheeky backheel.
Instead, Young scored what proved to be England's winner in the 68th minute, placing the ball past Sorensen after Glen Johnson had dispossessed Michael Krohn-Dehli in midfield.
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