Quote Originally Posted by Trampaige View Post
Page 65, PHB:

"P r o f ic ie n c ie s
Armor: Light armor, medium armor, shields (druids will
not wear armor or use shields made o f metal)"

If by explicitly not allowed you mean there are no penalties, sure. But your DM allowing you to do that is house rules.
No penalty and the language suggests that it is 'not done'. the line specifically says will nowhere does it say druids can't wear metal armour.