The design requirement for seats and restraints for light aircraft is for an occupant weight of 170 pounds. A person of a greater weight will have less protection from crash forces.
A client of mine spent ten years restoring a Tiger Moth to beautiful condition. I watched its progress, as a part time project in his hangar over that time. He always had a gleam in his eye when he spoke of flying it again. I was on the phone with him one morning discussing flying I would be doing that afternoon in another aircraft. At the end of the discussion, he passingly said "... and while you're here, I'll have you fly the Moth.". That surprised me, (a) as it was his pride and joy, and he had mentioned so often about flying it again, and (b), as I had only flown a Moth once, more than 35 years earlier.
As I arrived at his shop, there it was, ready to go, surrounded by his proud staff. He was nowhere to be seen. I sought him out in his office, as usually, he had "advice" for me before the check flights I flew in his [customer's] aircraft. All he said was "go take the Moth for a flight, and make sure everything is okay with it. It seems to have shrunk since I flew it last. The staff told me he'd tried to fly it, but simply could not get in. I flew it two flights, checked myself out in it, and had lots of fun. It was sold and gone within the week, without another word.....