Three men, age 70 to 74 finished Ironman Canada on August 25.
To me that says you can bike as long as you like. Just don't stop.

[h=2]All Age Group 70-74 Male Athletes[/h]
[TABLE]
[TR]
[TH]Name[/TH]
[TH]Country[/TH]
[TH="width: 60"]Swim[/TH]
[TH="width: 60"]Bike[/TH]
[TH="width: 60"]Run[/TH]
[TH="width: 60"]Finish[/TH]
[TH="width: 35"]Div. Rank[/TH]
[TH="width: 35"]Overall Rank[/TH]
[/TR]
[TR]
[TD]KOSTIC, Milos[/TD]
[TD="class: right"]CAN[/TD]
[TD]01:42:36[/TD]
[TD]06:45:48[/TD]
[TD]04:13:34[/TD]
[TD]12:57:50[/TD]
[TD="class: right"]1[/TD]
[TD="class: right"]1070[/TD]
[/TR]
[TR]
[TD]SCHWARTZ, Merrill[/TD]
[TD="class: right"]USA[/TD]
[TD]01:38:30[/TD]
[TD]07:14:18[/TD]
[TD]06:00:17[/TD]
[TD]15:15:53[/TD]
[TD="class: right"]2[/TD]
[TD="class: right"]1739[/TD]
[/TR]
[TR]
[TD]ENSSLEN, Dick[/TD]
[TD="class: right"]CAN[/TD]
[TD]01:27:09[/TD]
[TD]08:30:02[/TD]
[TD]05:43:16[/TD]
[TD]16:03:31[/TD]
[TD="class: right"]3[/TD]
[TD="class: right"]1870[/TD]
[/TR]
[/TABLE]