It's been stated as a fact that it's been 13 years since the formation of the Fantastic Four (at least as of 2006, it could be slightly longer now). Since Pete was 15 when he got his powers, and the Fantastic Four had been around for about a year at that point, that places Peter at around 27 or 28- give or take a year since we don't know the exact Marvel Universe time difference between Fantastic Four #1 and Amazing Fantasy #15, we don't know exactly how much "Marvel time" has passed since 2006, and little things like birthdays early or late in the year can make a difference in figuring out people's ages. He really can't be any younger than 26 or any older than 29, though.
Civil War is said to have happened 1 year ago. It is the 1 Year Anniversary of his Death in Thor.