Generally 70 is the age at which it becomes problematic for insurers to approve new pilots. The industry understanding is that pilots who were covered before they turned 70 will continue to be covered after they turn 70. Non-disclosure of age risks non-coverage!
Of course there are always exceptions to the rule, a 70 year old pilot being insured in J3 Cub will be more easily accepted than one flying something more complex and high performance such as an Aerostar or VLJ.
Not everyone ages the same, we have had pilots enjoy solo privileges into their early 80s. The way we accomplished this was by successfully arranging meetings between the client and their insurance company. The meeting allows the underwriters to see and talk to the client. Gauge their physical and mental capacity and, perhaps more importantly, their approach to safety.