oldest person in banking???

By the time you are super old and working for an investment bank, you usually occupy some ceremonial "Vice Chairman" job where you float in and out of mega-deals to add heft and annoy analysts and get paid obscene amounts of money to make phone calls and maintain strategic bank relationships. 

Why would someone ever leave that job willingly?

Bad with money? Addicted to the game? Don't know what to do with themselves without work?

The head of one of DB's product groups has to be in his late 60s 

Working in IB at that old can actually kill you I'm pretty sure, if you are still doing the same type of work.

At that point, it probably isn't about the money. Once a class of new analysts goes through years and years of pressure cooker distillation, there's naturally only gonna be like 2 guys left- and those are the guys who are doing this shit because they love the game. 

At my old bank (European BB in London) there were a couple of "Vice Chairman" senior advisor types floating around. The oldest of the bunch was easily in his mid 70s and had literally been an MD at the same bank since the early 80s. Rumours were that he had a 9 figure net worth which I find quite easy to believe given that most of his career was in the pre crisis glory days.

To go on for that long you have to absolutely love the industry and not have any ambitions to do anything else.

I work with guys in their 70s who still actively work on deals and leverage ancient relationships to bring in business. They're actually super chill to work with because they're already rich and just doing it because they genuinely like the job. Good stories from the "golden age" too.

Frank Gore just played a year with the jets. Some people just really like their jobs, I guess.