Being elderly isn't the problem as such, it's being less mobile - the problem is that 2-seaters have seats too close to the ground just as conventional 4/5 seater cars do, hence the popularity in CUVs and SUVs among the less mobile just because the seat is higher off the ground

Main problem I found as that the doors needed a lot of room to open wide enough to get out of. The number of times I had to squeeze out trying not to clang the car parked beside me and scrapping the bottom of the door because my foot was half trapped made me change the car.

Is it actually possible to have a used 2 seater which is OK for an elderly passenger to get in and out?

It certainly is. According to the UK definition, I have been 'elderly' for quite some time and still find it OK to both enter and emerge - or perhaps arise - if somewhat sluggishly, from my TR7 DHC. Indeed, despite some recent sciatica, I have just done so on this glorious calm day of September sunshine.

It isn't so much the seat height, most of these 2 seaters have similar heights but access to the seat, and maybe more important some room to swing your legs in, could vary by extremes.

Jaguar and BMW sports cars i found to be the worst by miles, getting out of a Z4 i'd end up rolling out onto my hands and knees, Jaguars, particularly XJS i used to struggle shoe horning my legs under the steering column into the tunnel that served as footwell.