How does an E6 have 6 service stripes?

Broken service, perhaps some guard or reserve time, there's a number of ways for that to happen, although nowadays with high year tenure, 18 years would be his last eligible year of service. In the navy we have a number of E-6's with 18 years of service, thy're good troops, not good at testing or in a rate that has slow advancement.

some mos rank is slower fact of life

My father was active duty Marine 1942-1972. The Marines hash marks are for 4 yrs each. 6 hash marks in the Marines would be 24-27 yrs. Dad had 7 & retired E-9 Mgy/sgt. 7 would be 28-32 yrs

Great Question a lot of NCO are E6 with 18 years nothing unusual most don’t make E7 in some MOS fields like Army Mariners rsnk is very hard to get because you must be licensed to grade to get the next stripe the average is 4 to 5 yrs

H may have been busted in rank

Got out after 12 1/2 because 10 of those were as E-6. Had four service and 5 combat stripes.

I spent 12 1/2 years in and got out because 10 of those were as E-6. I had four service and 5 combat stripes.

I retired as an E6 in the Navy. Yeah I had some authority issues but my leadership still thought I was worth keeping on. And on the subject of promotion. I was the ONLY crewman in a marking period to receive a Navy Commendation Medal from the Secretary of the Navy,... and somehow was still passed over for promotion in that cycle. If you LOVE your "job",... KEEP DOING IT, and do it to the very best of your ability. Your Country, your unit, those you report to, and any men/women whom you lead DESERVE that.

I was under the impression that each service stripe was for 2 years...

My dad had 43 years in service 1951-1994. He wore E-7 for 23 years.