The show does a good job at mixing the timeframes. We see the 1950 style cars in flashbacks of Stargirl’s stepfather. Watching along, there is a similar feeling that we get when we watch those popular ’80s films within the show as well.
However, there’s also a present day feel to the series in general and, adding in the special effects that give a future-vibe, it could stand to be in several years. It feels like a modern-day makeover of a superhero show that could have been super popular back in the ’50s as well. Other than the teenage female lead, which may not have played so well back in the day.
“There’s always changes when you adapt something,” he said in an interview with Inverse. Adding, “But the goal has been to stick to the lore as much as possible. Because it’s great lore. There’s a reason these characters stay in our imagination decades after they were introduced.”
Source : https://www.distractify.com/p/what-year-does-stargirl-take-place