The MC will improve somewhat in fighting and greatly in strategy and tactics as COM increases. I doubt the game will cover more than a couple decades, so age-related deterioration needn’t come into it; and while wounds could, I doubt I’ll code for that. Stat drops are a pretty brutal thing to code in when you only have 7 stat points for a whole campaign.
0 is low-average… weak like most normal people are weak at many things. You’re not a dolt at INT 0, cripplingly clumsy at COM 0, or scaring children in the street at CHA 0. You’re just normally flawed. Like many normal people in any era who would quickly die in combat, or struggle to convince a stranger of something, or find it difficult to hold lots of information in mind.
The other stats are portmanteaux too – e.g. INT covers memory as well as cunning, CHA persuasiveness as well as raw personal magnetism – and NPCs won’t necessarily come with the whole package any more than they do with COM.