Congratulations on the golf result PJM.
I see you enjoy the fast run down Sanderstead Hill as much as I do, and your suspension probably eases you over those harsh ridges across the wide top stretch. I just get my teeth rattled!
On the gearing, I'd say stick with it for a short while since your improving fitness might make change unnecessary. If after a while you find change still desirable, there are other cassette choices spreading thr gears a bit wider or the megarange sets with a very low first gear. A wide range is better than megarange usually though, avoiding the big jump between the lowest two gears. Either way, a larger bottom gear sprocket often means a change of the rear mechanism as well, since standard ones often cant handle the jump. Doesn't cost much though, a Shimano Acera rear mechanism works well on large sprockets and costs around £15 last time I looked.
Many people exceed bike weight limits without trouble, the makers are always very conservative in their ratings. On your disc brakes, mechanically operated ones are generally not particularly strong, though there is the odd exception like some Avid models that are liked. A change to hydraulic is a bit complicated and expensive, but if yours don't improve as they run in, maybe a change to a recommended Avid cable operated model might help.
I very much agree with your last paragraph, government's attempts at social engineering with the aim of protecting the young have been as bad as all such attempts always are, resulting in a new form of deprivation and long term behavioural ill effects. A Wii, X box or getting senseless on alcohol is no substitute for a full life.
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