The phrase (not sentence) 'long-standing army' is grammatically correct. It means 'an army that has been established for a long time.'
There is a guru standing on my toe.
"They were as tired and depressed as a defeated army."
The boy was standing on the platform.
Not by the British Army, as they left Austria in 1955. The buildings are still standing and may be in use by the Austrian army.
Officers carried swagger sticks.
Yes if you use it correctly, as in "i enllisted in the army"
He was wearing an army garb.
The army had a postwar celebration.
The former "Silas B. Hayes Army Hospital" at Fort Ord is still standing and in use. As to what use - I do no know.
I was really shocked to see the bruin standing before me..
After the Nazis Army was incapacitated, they retreated.