Lauri Törni (aka Larry Allan Thorne) not only fought in multiple wars, he also wore the uniforms of three different countries:
Thorne enlisted in the Finnish Army in the 30s and became a Captain. At one time, he went to Germany and became a Untersturmführer (lieutenant) in the Waffen-SS.
After WW II, he emigrated to the United States, enlisted in the US Army and eventually became a major in the Special Forces. He was killed in action in Vietnam on 18. Oct. 1965.
Thorne fought in the Winter War between the Soviet Union and Finland in 1939/40 and in the Continuation War between the Soviet Union and Finland from 1941 to 1944. While in the US Army, he, somewhat ironically, again was stationed in Germany and lead a rescue mission in the Zagros Mountains in northern Iran. Thorne then served multiple tours in Vietnam where he died in 1965.
His remains where not found until 1999, he is now interred at Arlington National Cemetery.
George Bush was discharged from the Navy in 1945, and then served as Commander-in-Chief during the Gulf war, which makes a gap of more than 45 years between wars.
Several people in my unit served for Vietnam, Grenada, Panama, the first Gulf War, Bosnia, and post-9/11. Two of them topped out at the maximum enlisted time of 42 years (mandatory retirement at age 60).
My grandfather, born in 1898, served in combat in both world wars. Lied about his age both times, and was accepted both times. He wasn’t the only one, there were quite a few who did the same, former Gallipoli/Western Front ANZACs signing up for WW2 and fighting in both North Africa and the Pacific. My grandfather fought in all four of the theatres I just mentioned.
My mother was born in 1929, when my grandfather was in his early 30s, and I was born in 1965, when my mother was 36. My grandfather survived both world wars but died a year or so before I was born.
My uncle did the same thing. He joined the Marines when he turned eighteen and fought at Iwo Jima. He fought in Korea and was mostly stationed in Japan for Vietnam, though he apparently did make it into the country at some point.
Korea does not really count, it started less than five years after the end of WWII and many soldiers were recalled WWII vets (the mid level officers would have been WWII Vets as a matter of course). Some Korean War Medal of Honour winners who had fought in WWII
Jackie Fisher was Admiral of the Fleet in WWI, until he was driven nuts in 1915 by Churchill over Gallipoli. He’d started as a midshipman in the Crimean War of 1854, under Lord Raglan; who’d fought in the Napoleonic Wars.
Also at the Crimean War was the mascot on the HMS Queen: Timothy the (female) turtle, who died in 2004, aged approximately 161.
I had read of a Southerner who’d ridden as one of Moseby’s Raiders as a teenager, then went to France on WWI in his sixties, but I couldn’t retrieve the cite.
Unfortunately, the video is currently not available (or at least I am too dumb to find it). I remember how Col. Keirn compared his experiences as a POW in Germany and in North Vietnam.
There’s also my father-in law - recruited to the Israeli army in 1968, he served as a regular officer and as a reservist in every subsequent Israeli military action, and, as a Lieutenant Colonel, still does regular reserve duty at the age of 61. That’s 43 years. He’s always threatening to retire, but I don’t think he ever will.