How old is this Spiewak & Sons G-1??

I just found this G-1 at Goodwill and am not sure of it's age. It's in great condition, leather is definitely goat and has some fantastic grain in it. But it feels rather thin compared to the other two I have. I'm sure the collar is Mouton but it's kind of a natural color. Has a wimpy Scovill zip but works great. No tears or snags in the knits or leather. The label is a little hard to read in the pic. It says:
Jacket Type G-1
us navy
Bureau Of Aeronautics
SPEC 6101 (AER)
Contract # 6850...

How old is this Spiewak & Sons G-1??