No you can’t just join at 55, but he had served 14 years in the Navy, so that 14 was deducted from 55 giving him the chance to continue his military service without asking for an age waiver, that may not have been granted. All years completed with completed points for retirement are recognized as years completed.
A reservist can collect a pension at age 60 if they have served 20 years. He was able to get in under the wire using his 14 years, and save his chance for a pension later. Albeit that pension will be smaller than a full time military personnel. His twenty years will be finished at age 62, hence his statement that he would stay until age 62..and that is how it works.
That is exactly what he was trying to get accomplished. Another article I read indicated they had children who they wanted to help in college. So getting 6 more years would help his retirement.
Regardless of the reason why he did it, if Army boot camp is anywhere near as tough as it was in 1973, he’s one tough SOB.
I do not know how much smaller, but when I first started collecting my full time military pension, it was a whopping $761 a month. COLAs have made it $1,400 a month, but I would not do it again as an enlisted man. As an officer I would, but not as enlisted. It was hard serving under Jimmy Carter. I can not imagine how awful it is, serving under the Obungler, and it will be as bad or worse, serving under the Hildebeast after that.