Set the youngest and oldest age you need and get birth dates that land inside that band, with the age printed so you can check the fit.
Most tools that generate birthdays ask for a year range, which is the wrong end of the problem. What you usually need is an age range (users between 18 and 65, say) and converting that to years by hand means recalculating every time the current year changes. Setting the age bounds directly and having the year derived from them means the generator keeps producing correct data next year without anyone editing a fixture. The age is printed alongside each date so you can see the result matches the band you asked for rather than trusting it.
Age-gated features fail at their edges, and a random spread across a wide band rarely lands on them. If a feature opens at 18, the interesting records are the ones aged exactly 18 and exactly 17, including the person whose birthday is today and the one whose birthday is tomorrow. Set both bounds to the same age to generate a batch at exactly that age, then check the behaviour on either side. That is a much better use of the tool than generating a hundred users spread across forty years and hoping one lands somewhere useful.
Because age is usually the real requirement, and deriving the year from it means the fixture stays correct as years pass rather than drifting out of date.
Set the youngest and oldest age to the same value to generate a batch at exactly that age, then repeat one year either side of the threshold.
It is calculated from the year, so a record can be a few months either side depending on whether the birthday has passed this year.