Half the population is erased and then ultimately resurrected 5 years later. After the 'reverse snap' is the resurrected population now 5 years older or were they restored to the same age they were at the time of the snap, essentially jumping forward 5 years in time?
3 Answers
No, they did not age!
The Russo Brothers explained this in a recent interview with QQ (English translation on Reddit):
Q: What about those people who got dusted? What did those five years mean to them? Why didn't they grow older when undusted?
A: Yes, those people whom was lucky to survive the snap are 5 years older than the people who just got back. The reason Spider Man saw his friend again in high school at the end was simply because his friends was unfortunately also dusted like Spider Man was. Of course, there are people in his grade whom didn't die and they are probably already in colleges by now. To those dusted people, they had no conscious in these past 5 years. They didn't know what happened. It's as if they had just woke up from a long sleep. The only one who was aware about how many years has passed was Doctor Strange, because he has already seen that when he was time mediating on Titan. Parker's reunion with Ned was a touching moment. There are also people whom indeed moved on but suddenly was reunited with their lost ones. Yeah it's kind a complicated world now.
As Peter explained to Tony in his own unique way in the middle of the final battle he and the other 'vanished' simply came back without any awareness that time had passed and Doctor Strange explained to him that 5 years had gone by.
Based on Spidey, it's pretty clear they didn't age: Peter's young enough that a 5 year age difference would be highly obvious, but he looks identical to pre-snap Peter. There's also the scene at the end where he goes back to high school: if he had aged, he'd be too old for high school.