What's wrong with 70 year olds??
There are plenty still running their own businesses, lots still "working" on charity committees, school governors, etc. Our neighbour had a 70+ builder to build their extension!
It's not "age", it's health and fitness that matters.
There are plenty of 70 year olds who are as fit as someone half their age, especially with the obesity epidemic affecting the young!
I think we need to start looking at bringing back adult education, re-training for adults, etc., rather than spend nearly all the country's education and training budget aimed at 16-21 year olds. We need to have more opportunities for older people to retrain and change careers, especially those in "manual" jobs who need to settle down into a less demanding/physical job.
Most of my elderly clients running their own businesses set up self employment specifically because they needed a career change as they got older, particularly in their late 50s, and most are working in a completely different trade/profession as an elderly self employed person compared to what they did in the so-called "prime" of their working lives.