As a kid you were presumably playing near nettles a lot more frequently, and as a kid you're also a bit lax with being aware of your surroundings. Life was more in the moment.
This is it, I’m pretty sure. I had plenty of brushes with nettles as a kid, but I’m not super aware of them to be able to avoid them as an adult. However I spend less time in high grass and forests, since I need to be present in the spreadsheet factory, and when I do make it into the wild, I usually wear pants and the like to avoid scratches, ticks and poison ivy; so less likely to get nettles.
Side note: we bought some nettles from a local farm last year and made a couple dishes with them. Pretty tasty, if you already like tho ha like spinach or mustard greens (think saag paneer)
If I want to go for a hike, or even for a short walk in my back yard, it's a choice between slathering myself in bug spray or being eaten alive by chiggers. I choose neither.
In the United Kingdom, an annual World Nettle Eating Championship draws thousands of people to Dorset, where competitors attempt to eat as much of the raw plant as possible. Competitors are given 60 cm (24 in) stalks of the plant, from which they strip the leaves and eat them. Whoever strips and eats the most stinging nettle leaves in a fixed time is the winner. The competition dates back to 1986, when two neighbouring farmers attempted to settle a dispute about which had the worst infestation of nettles, and one of them said, "I'll eat any nettle of yours that's longer than mine."
Because now you know what the bastards look like and check for them whenever you're somewhere they might grow. I sat on one once and I don't want to go through it again.