The phrase "young deputy" is correct and usable in written English.
It is often used to refer to a deputy or other public official who is relatively young in age. For example: "John Smith was elected to the city council last year. He is one of the youngest city council members ever, serving as a young deputy for the citizens of his district."
"He thinks it's a new medium and that it's here to stay," de Young deputy director Richard Benefield explained of Hockney and his interest in the future of iPad art.
But his young deputy is stealing his thunder – spectacularly.
When it was over, Major Rong's young deputy, Captain Song, sought us out.
Eduardo Madina, the young deputy leader of the parliamentary party, may be too green.
Arnaud Montebourg, another young deputy, said it had "fallen into formaldehyde".
His young deputy, Terry Mattheww A. Brown, a star of "God's Army"), protests.
Defense attorneys portrayed Brunsting as a young, immature deputy thrust into a position of teaching other deputies early in his career despite having no training on managing mentally ill inmates.
As he nursed his wound at home, day-to-day editorial responsibilities fell to his young deputies, who carried on his cries for immediate action (presumably with their boss's endorsement) at an increasingly hawkish pitch.
Surrounded by a nervous posse of young deputies, the middle-aged Daggett disarms Bob and with a sadistic glee destroys him physically and mentally as an example to others.
My wife was speaking to the young deputies about the importance of nonviolence and explaining why they should be at home reading to their children, when one of the deputies reached out, shoved my wife in the chest and knocked her down.
After his election, he was among the leaders of a group of 15 young deputies viewed by the media as non-aligned.
