Speaking from a PI perspective, 26 is definitely not uncommon!
Just on my team the past 6 interns in our area (including me) have had ages ranging from 21-34, with only 2 of us being just out of undergrad. The other 4 were 26, 29, 29, and 34 and all in masters programs.
My area may be an anomaly (there are plenty just coming out of undergrad) but it seems to be common for PI's to have a wide age range