They have a smaller window for their careers then men do, who can age "gracefully" and still act/sing/etc. If you have a voice like Celine Dion as a diva you can keep performing forever, but for most female singers, your career is mostly over by your mid-30s because so much of your brand is actually based on your looks too.

Meanwhile, your biological clock is ticking. If you want kids, your window is closing down.

It'll be interesting to see what Taylor does next, if she shelves her career to have a family while she still can, or if she keeps riding the incredible career success she has had and sacrifices the ability to have kids along the way. Kind of a brutal choice. It's different for men who, like Bill Bilicheck, can always date a younger girl later on and have a family if they want to, and where, like Sean Connery, growing older can actually be part of their charm and good looks.