Did Sam Shepherd, actor and playwright serve in the US military

Not according to biographies on Wikipedia or biography.com. See: https://en.wikipedia.org/wiki/Sam_Shepard or https://www.biography.com/people/sam-shepard-9481676

I wonder why...

His father was in the military but was alive til the mid 80s. Sometimes you could get a deferment for reasons having to do with sole support, etc. I don't know.

I wondered that as well. He was born in '43 so would have turned 19 in 1962, which was before the draft seriously escalated for Vietnam in 1965. In the mid-60's it was pretty easy to get a deferment from your local draft board - just ask Bill Clinton or Joe Biden about it. He was too old to have been included in the first draft lottery in 1969.

I was born in '46. Nobody got out easily around where I was. I know one of each type for 64-65: CO, starvation (medical), fake crazy (didn't work for everyone), and go to Canada. I think the CO also happened to be 'sole support of mother and siblings' or in those days, 'sole son of family who's father had died.'

I'm not going to wonder so much about Sam. I have wondered quite a bit about that right wing loud mouth James Woods. ALL mention of those years wiped out, everywhere. He sort of drops out of MIT and vaguely drifts off into theater thanks to somebody famous.