At 42 I remember the pre-sunscreen days as well. At the beginning of summer we would all go to the pool and get a nasty burn. Within a week we were at the pool all day every day and would not have a burn again until the next year. On average we would be getting around 3 painful but not serious burns per year (one at the start of summer, one when we went to the amusement park, one when we went out on a boat or something) despite hundreds and hundreds of hours of direct sun exposure each summer.

These days I rarely spend much time outside in the sun, and when I do I almost always burn. I am not in the sun enough to maintain a tan. When I go on vacation I can build up to about 4 or 5 hours of full sun exposure without burning in about 2 weeks (if I get outside a few weeks before to kickstart things), just in time to come home and lose my tan completely. As a result, I get sunburns more often now than I did as an 8 year old when I spent more than 40x more hours in the sun every year (roughly 4+ hours per day for 100 days of summer weather, vs today where it's maybe 20 minutes every few days).

I guess my hypothesis is: much less cumulative exposure can result in more damage to DNA if it is punctuated by periods of intense exposure when compared to consistent intense exposure.