Alternatives to Traditional Retirement

With a wealth of experience in your field, you might know precisely what is missing/wrong with your market or industry and be in a position to offer a solution. This doesn't seem appealing to me, as most entrepreneurs work even harder and more intensely than an employee with an established company.

Make jam, woodworking or even convert unused rooms in your residence to an AirBNB.

The (somewhat) formal dividing line between full-time and part-time work is 30 hours per week. If an employer can accommodate this, it might be suitable for many, however, the formal structures also mean that if the expectation is 25 hours a week, that should be a consistent expectation for both sides (employer and employee) which may be a bit rigid for a semi-retiree (or maybe I'll call them 'pseudo-retirees'?)

Advise, mentor, train and bill for your hours. The most likely client would be your former employer. Hopefully this would allow the most flexibility, but if the client needs to have you on call when you'd rather be on the beach, a retainer fee would be a lucrative solution.

Fixed-term contracts also exist, so maybe you work for 6 months at a time.

Continue in your existing role, with full-time work week, but your absences can be on the order of months rather than days or weeks, and of course, they are unpaid, unlike vacation days. The management would have to find ways to cope with extended, yet temporary absences, but with several pseudo-retirees on staff, they could rotate their extended absences...

Most parental leave is absolute, but in theory, a granular reduction in hours might be desirable to some. If a new parent cut their hours in half, and a pseudo-retiree did too, they could split the payroll expense, in theory. This could apply for interns/co-op students who have to keep up with classes too.

I'll bet most jobs have a combination of 'fun'/inspiring elements and tedious drudgery. If the drudgery/paperwork elements were outsourced to interns or virtual assistants, and that expense were subtracted from the pseudo-retiree's pay, their effort would be limited to where their expertise was of most value, and free up their time for leisure, etc.

Alternatively, if the pseudo-retiree is a knowledge worker who doesn't feel like doing the intellectual heavy lifting anymore, they could stick to the simple, tedious tasks on a time-limited basis.

The retiree works remotely 100% of the time.

These kinds of activities fall within the traditional model of retirement, but if a pseudo-retiree stays engaged with their employer and heads up a company initiative based on community engagement or environmental sustainability efforts, they might be able to leverage their network and expertise for the greater good.