I'm in my 30s, and I think that dressing trendy has nothing to do with age. There are trends that might be suitable for older people, and there are trends that are suitable for younger people. And there is no reason to shy away from trends that read young anyway, if we choose.

Maybe most older people shy away from mini-skirts, but there are so many reasons to embrace midi-skirts (which are more popular now). Maybe see-through plastic jackets are not suitable, but blazers are very very good. Especially since recent fashion gears toward modesty and muted styles, there are just way more styles suitable for older people.

The thing is to keep up to date with trends. I watch instagram posts of people who are younger than me to keep up, and I read Manrepeller a lot. Many of the women on the site are trendy but dress age appropriate (in their 30s).