One of my riding mates is over 70yo, 5'7" and is very comfortable on his 1250GS with factory low suspension. In the last 3 years, we've done well over 10,000 miles on tours together. He loves it.
I'm 5'11", 31" leg, in my early 60s. I had a standard 1250GS. Easy flat foot, with a bend in my knees. Initially the standard seat was uncomfortable, but was spot on if I put the front of the seat on the high setting, the rear on low. After many years of Japanese and Italian bikes, I was and remain, smitten with the BMW build quality and boxer motor. In 2024 I went to a 1250RT and regretted it, the knee bend was uncomfortable after 100 miles. I'm now (since April) on a standard suspension GSA 1300, with adaptive height. The moment I took out a demo 1300GSA, I felt I was home.
That said, for the mix of touring ability, torquey performance, light handling, comfort and character, I think the 1250GS was peak BMW. If you can, try the lowered 1250GS, it may seduce you! However, you may be nearer £10k, than £7k for an earlier 1250. From a main dealer, it comes with a comprehensive and extendable warranty, which includes repatriation / breakdown assistance, for peace of mind.
Good hunting!