According to a book called "cooperation under anarchy". It talks about thousands of priests and nuns mobilizing under Protestant Germany, Catholic Austria, Orthodox Bulgaria and Moslem Turkey. On the other were Protestant Britain, Catholic France and Italy, and Orthodox Russia. They fought both sides.
World War 2
pad
Yes, many did.
You had to be 18 to enlist for the British Army in World war II, though some boys who were younger were able to enlist using false documentation.
They encouraged people to enlist
To encourage people to be brave, help with the war effort at home or enlist in the Army.
after the war started, of course, the answer actually depends on which country you are talking about.
Not in the army, but as a nurse.
I believe there was was a Frenchman, aged 84
1914
propaganda posters
35 years old