I think that jeans and a T-shirt is perfectly normal casual, lounging around-wear for just about everybody. The issue isn’t really one of violating some sort of unspoken ageist dress code. It’s more about the fact that your values and self-image–and, therefore, the impression you want to give others of yourself–changes over time.
I’m 30. I spend most of my time in jeans and a T-shirt. When I’m wearing something other than that, I like to wear clothing designed for women in their 30s. (Actually, what I’d really love is a wardrobe of custom-tailored salwar kameez. But until I make it to India, or earn a lot more money, that’s out of the question.) I think it makes me look like I’ve developed a certain healthy maturity, reserve, self-discipline, and achievement that going to seminars in capri pants and oh-so-cool Abercrombie and Fitch tees simply wouldn’t convey. I get the feeling that clothes for women older than 25 emphasize self-confidence and self-acceptance–and with that self-confidence and self-acceptance, I think, comes some modesty. After a period of experimentation in your teens and 20s, you don’t need to have the entire world appreciate your flat belly, your rebelliousness, or your insouciant coolness. You know you’re appealing and passionate, but you’re willing to let that be an unspoken fact, rather than a statement in need of corroboration.
Clothing made for 25-and-under women tends to say, “Look how cool/independant/rebellious/physically appealing I am!” while clothes for women older than that tends to say, “I’ve had some growth experiences, I’ve developed good taste, a healthy sense of discretion and of what’s really important in life. Respect me for the knowledge and experience I’ve earned.”
I think most people assume that you don’t have the need to be as forward about yourself as you get older as you did when you were younger. People assume that a well-adjusted, post-25-year-old is going to have come to a more secure and well-formed identity, and that your clothing is going to reflect that. (I think people also expect that your body language is going to change to reflect that, too. That’s why some women in their 60s can get away with some clothing styles that usually associated with much younger women; the body language of these women tends to reflect a lot of confidence, so the fact that the clothing is more typical of 20-year-olds doesn’t matter.) When people in their 40s are projecting a sense of identity that’s more usual in a twentysomething, it seems that there’s something amiss with that person’s life. I think that’s ultimately why people feel that different styles of clothing are appropriate for people of different ages.
Wow–I can’t believe I just wrote a good 3 paragraphs on clothing. I must really, really, really not want to study tonight. 