I passed a team yesterday I know. Captain is probably 10 years my senior, so 77. (We did 50 miles together on singles ~13 years ago.) Guessing his wife is two years younger, that makes ~152 years. Their bike is their second tandem, custom for them in the early 90s from Davidson. So I'm guessing they been a team since say '85. So beginning Tandem Years = ~82.
I'll have to tell them about this next time I see them and update this with the real numbers. ( I see them about every 4th ride or so. They are true regulars. Their total miles have got to be huge. The bike's paint is testimony. Red fading to purple. The red is VERY faded.)