Now, Franklin may have been a bright chap -polymath, politician and a Founding Father of the United States - but speaking as someone squarely in his forties, I'm not sure I agree with him that my judgement is any greater (or, thankfully, diminished) as a result of racking up four and a bit decades on life's odometer.
Furthermore, it should be pointed out that Franklin was in his mid-forties when he famously flew a kite in a thunderstorm to prove that lightning was electricity - an experiment that could hardly be described as demonstrating sound judgement!
So, if it isn't 'judgement' which reigns at 40, what is it? Well, if a recent study is to be believed, it's 'fear'.
Since the beginning of last month, employers have been banned from issuing notifications of retirement using the Default Retirement Age (DRA) procedure. This is part of the government's programme of phasing out the DRA, such that from 1 October this year, compulsory retirement will be outlawed unless it can be "objectively justified" on the basis of individual circumstances.
When the Government announced its decision to scrap the DRA last summer, the knee-jerk reaction of some employers' groups was to warn that this could lead to employment tribunal cases from older employees who had been dismissed rather than allowed to retire. This may still prove to be the case. However, as the implications of this decision have slowly sunk in, it seems that the greatest concern now sits with employees rather than employers.
At the end of last year, market research company GfK NOP interviewed over 2,000 UK adults and found that the majority of people over the age of 45 were pessimistic about the impact abolishing the DRA would have on them. This is a particularly worrying finding, given that this group - dubbed the 'Fearful Forties' by the researchers - will make up more than half of the workforce by the end of the decade.
The fearfulness seems to be rooted in two main concerns. First, respondents perceived limited opportunities for progression with their current employer. Second, they feared that if they became unemployed in their late fifties they would end up being 'stranded' there.
As the researchers point out, these perceptions have worrying implications for employee engagement - I would add health and wellbeing too - that employers need to address.
The great news, however, is that in recent years many employers have already either voluntarily scrapped the DRA or, where individuals were willing and able to continue to work, taken a very relaxed attitude towards its implementation. In doing so, there have been clear benefits for both the organisation and its people.
At the heart of their success has been a formal and informal performance review process where staff of all ages can discuss the working patterns that meet the needs of the business while enabling them to fulfil both their career ambitions and their aspirations outside work.
For me, this makes an enormous amount of sense, because, as individuals move between key life stages, what they need from work changes - as do the workforce needs of employers at different times of the year and at different phases of the economic cycle. As a result, by engaging employees in a regular dialogue about their mutual needs, these enlightened organisations have created a highly flexible workforce and retained key skills through challenging times.
Consequently, this progressive, post-DRA approach is one that those of us in our forties should view less with fear and more with excitement. After all, research shows that 60% of us would like to continue working past the default retirement age if we could have more flexible contracts - while the prospect of tapping into a skilled, experienced, highly flexible pool of labour is clearly very attractive to employers.
So, if at 20 years of age the will reigns; at 30, the wit… what does reign at 40, if not judgement or fear? Well, I would like to think it's the mind. Because, as the growing number of older people in the workforce prove, age is an issue of mind over matter. If you don't mind, it doesn't matter.