Page 45 of this PDF has a good chart. It shows that about 26.8 million men were draft eligible in that generation, and about 8.7 million enlisted, 2.2 million were drafted, and 16.0 million never served, including about 570,000 apparent draft dodgers.

About 2.1 million actually went to Vietnam, and about 1.55 million were in combat roles in Vietnam. 51,000 were killed.

So roughly:

• 41% of that generation of men were in the military
• 8% of that generation went to Vietnam
• 6% of that generation fought in Vietnam
• About 0.2% of that generation died in Vietnam