Call this culture shock, if you like, but when I came to live in the US, I noticed this thing: Older (or should I say "elderly") women wore trousers. And even shorts. *gasp* Now, let's put this in context.
My grandparents were born in the '30s or thereabouts. So, people from that generation had very strict ideas about clothing. I would say the rules are more relaxed with each new generation, but people from that generation tend to be very conservative. Given the era that they grew up in, modesty was the rule. More importantly, I think the aversion towards trousers was heavily influenced by both culture and religion.
I don't believe I ever saw either of my grandmothers wearing trousers. Shorts ke? Abomination! They usually wore iro (wrappers) and buba, skirts and blouses or dresses.
I am not saying that all African/Nigerian grandmothers wear wrappers or gowns all the times, but I believe most of them do. Or better yet, I would say you are more likely to find an American or European grandmother wearing trousers, than you are to find an African grandmother doing the same.
Have you seen Nigerian/African grandmothers wearing trousers/shorts? Do you think its odd?