Most are pretty safe by the time they are 5 months old. Owls are capable of clipping off a human finger with one bite.Are they safe from owls after ~5 months old? I have removed the head of an adult male before....I would not describe it as "click". Owls must have superhuman jaw strength.
Trying to figure out what to make for turkey nighttime house...I take it they don't like walls. Maybe a chain link dog kennel with a roost?
Some people make a 3 sided lean-to for their turkeys.
I believe that @Huntmaster uses something similar to what you are describing.