Actually, that was pretty rare for colonists.
As for the view that they were old, I think that is mainly the fault of portraits. Not because they were inaccurate, but many times they were painted much later in life. Henry Knox looks very old in his most known pix, but he was only about 25 when it ll started.
Worse, it seems even our media have perpetuated what the portraits started. Movies and shows, and even documentaries, often use oldsters to represent these people. Washington is the worst offended, perpetually shown as old and white haired. But he was only about 51 when the war officially ended! He was only 69 when he died.