It would make sense that the older your get, over 35 or so, one would require less in terms of dosage as his natural test production is much lower than say a 25 year old. Thus, the effect of injecting, say 500mg enanth/week would have a much stronger effect than the same dosage on a 25 year old.

Sample numbers for the sake of an example:

35 year old
free test level of 100mg
inject 500, net 400 jump

25 year old
free test level of 250mg
inject 500, net 250 jump

Makes sense? Any ideas?