Scion of Murgen (He/Him)
The challenge with this approach is not letting it turn into simply a min-maxing tool. Generally speaking, in D&D it's more important to be good at your specific thing than at everything. Similarly, being able to raise your most important ability score is much more helpful than lowering some other ability score is detrimental.Not necessarily, as I mentioned upthread the full idea was you got the +1 for a -1 only if you wanted to. Otherwise, it is assumed you are working to keep your "weakness" from developing into a weakness.
Either way, you might increase STR but lose DEX or CHA or whatever. You might increase INT but sack WIS as you lose touch with the world around you but study more, or how ever you want to work it.
If I were trying a +1/-1 aging system I might specifically require the -1 to be applied to either the character's highest or second-highest ability score. Or just always to Constitution, which would help simulate increased fragility and vulnerability to injury. In the latter case, to counterbalance the min-max effect, I might actually make it -2 to Con.