Early 50's is still young enough that for steroid cycles (I don't have an experience base for MAG-10 use with men of this age so will have to go with anabolic steroid use) I don't think there's a need to adjust dosage except where there are specific health concerns. The most basic one is high blood pressure: blood pressure should be monitored and if a given dose gives an increase that is of concern, then decrease the dose.
It's common for anabolic steroids to increase blood pressure, and while at any age an extreme increase ought to be avoided, I tend to feel a younger person can get away with things that an older person would be wiser to avoid doing. I can't give hard and fast numbers on it but generally I'd say that if there is in the first place a systolic of 140 or above or diastolic of 90 or above then no large increase should be tolerated, and if blood pressure is already well above those figures then little to no increase should be tolerated.
Also for an older man it is more important to avoid increasing estrogen at the same time as increasing androgen, as that is a bad combination for the prostate. MAG-10 does not increase estrogen, so that isn't a problem. There can still be decreased urinary flow after a number of weeks of an anabolic steroid cycle that doesn't increase estrogen, but ordinarily this reverses not long after the cycle is over.
Supplement use doesn't really differ from non-cycle use, but cost/benefit can differ. What I mean by this is that, for example, an individual might be at a place where he has been training consistently and well with good nutrition and supplementation for some time, and regardless of trying to improve his training in various ways further gains have been coming very slowly.
In this case, if $X/week on supplements produce a really significant boost in results, then depending on financial circumstances this may be seen as an excellent return on money.
But on the other hand, if an individual is where he has good gains coming anyway without any particular supplementation, then a further increment with the supplementation might well not seem worth the same money, as the lifter was quite happy with his outcome anyway.
With the MAG-10 use it might well be the case that very extensive supplementation would yield some significant (even a pound is significant) extra muscle versus what the cycle would have done anyway, but because the results without it would also be very satisfactory, the increase might not be thought to be worth the money.
But on the other hand, some are well able to do it, and prefer to things the best they know how, so for them it is well worth it.
So it's very much an individual thing.
If choosing to keep the cost moderate, I'd put the first priority at improving protein intake, for example with Low Carb Metabolic Drive.
At the next level up, I'd use Anaconda, MAG-10, and Alpha-GPC as well.
If going all out or if addressing specific issues such as inflammation, I'd add Curcumin-500, ReceptorMax, Flameout, and/or Rhodiola.
An age specific difference, probably not related to gains in a cycle but just in general, is that as one gets older need for the essential fatty acid GLA increases, so the FA3 supplement will be more relevant than would be the case for say a 20-year old.