Sorry to resurrect an old thread, but unfortunately I missed it at the time and it has only just been pointed out to me on another thread.
I suppose 75 isn`t bad really, but, as we used to say in my National Service days - get some service in laddy. It may well be that I haven`t the punting experience of the OP, as I only started out of loneliness a year or so after my wife died and after 50 years of very happy married life, but it has been a fairly steady 7 years or so of regular punting since then.
I am now 86, still punting regularly (although I stick to a regular who suits me down to the ground), I don`t need pills of any sort to get me up to speed and can go for an hour when I wish to. When I can no longer do this on my own, then I can fall back on the little blue pills, and they should keep me at it for another few years, so all in all, and with a bit of luck, I expect to be interrupted `on the job` to be told the telegram has arrived from Her Majesty in 14 years time.