Barbara Trombetta can count on one hand the stores where she finds clothes that actually fit her.

The 47-year-old Boston public schoolteacher says she is frustrated with tiny shirts and tight-fitting pants that don't flatter her middle-age figure.

"It's really hard," Trombetta said. "I've got money to spend, but there are not a lot of places to spend it."

But if merchants have their way, Trombetta won't be complaining for long. Once considered uncool and unsexy, the apparel market for older women is hot. These women are growing in numbers, and so are their purses: By 2010, women 45 and older are expected to unseat teenagers as the biggest spenders on clothing, shoes and accessories.

Indeed, retailers think 45 could be the next 15: Over the next year, companies like American Eagle, Gap and Gymboree are expanding existing concepts aimed at older women or unveiling new ones. Hingham's Talbots is making the biggest bet, proposing last month to buy Quincy rival J. Jill for $517 million in a bid to create the nation's largest specialty chain catering to women over 35.

"A lot of stores basically walked away from the older woman," said Marshal Cohen, chief retail analyst for NPD Group, a market research firm in Port Washington, N.Y. "But the teen market is being sliced so thinly that retailers need to regroup. And stores are finally beginning to recognize that this is a customer who can no longer be ignored."

What's made older women attractive? Namely, many of the 40 million women of the baby-boomer generation who are now in their 40s and 50s. The group's sheer size will increase the overall spending in the $101 billion female apparel market. And unlike past generations, women have more disposable income and are willing to spend it on their looks, merchants and consultants say.

That's in part driven by women waiting until their 30s and 40s to have children whose fashion sense can rub off and encourage parents to routinely update their own wardrobes rather than just buy new clothes when it becomes a necessity. Add to that higher divorce rates than a generation ago, putting more women over 35 into the dating scene, where they want to look their best and stay in style. Hollywood and television shows such as "Desperate Housewives" are also promoting the middle-age woman as sexy.

"This generation refuses to grow old and dress like their mothers," said Olga L. Conley, chief financial officer for J. Jill, which appeals to older women with its casual style of loose sweaters and flowing skirts. "We are trying to grow this chain as fast as we can so by the time other guys come in, we're a force to be reckoned with."

It's a necessary strategy as more competitors look to older women to boost sales as malls become overrun with teen retailers, including Hot Topic and Abercrombie & Fitch. Even companies that indulge youth are growing up: Gap Inc. launched a new chain, Forth & Towne, last year aimed at women over 35. Children's clothier Gymboree Corp. started Janeville in 2004 to cater to older women; today it has 16 stores, including one at Chestnut Hill's Atrium Mall. And teen chain American Eagle recently announced it will open the first four stores of its new Martin + Osa brand targeting older women this fall.