I don't think this is true in MM1. MM1 also has a way to change character's genders, which I used to make eveyrone female to deal with Portsmith. Then I think I left them that way for the rest of the game and never had any problems. But of course, if it is a problem, one can change characters' genders again.

Also, in MM2 characters will indeed age if a full in-game year goes by, but in MM1, characters only age by leveling up (one year of age per level) or by artificial aging, which can occur when facing certain monsters (I think... definitely true in MM2, not as certain about MM1) or by casting certain high-level spells. So if you are trapped in Portsmith, you would be unable to wait for old age, unless every character had the ability to cast spells that age them, which is unlikely (usually only priests can cast these spells). Also if you're high-level enough to have those spells, then you should have teleport and etherialize and can escape anyway.