That's not really the point. Older people can have style, too, but something more sober is expected of them. Older adults who dress like teenagers will be seen as immature. For example, punk people might ditch the mohawk, wood glue made, coloured spikes for more subtle colourful highlights. Skater-like people might add an open button shirt over their favourite t-shirt, etc.
Everyone can have a style, but denying the influence of age on it isn't very wise, if you ask me. And no matter what reason says, sometimes a very bold look can look "daring but cool" on a young woman, but give the very same outfit to that person's mother, and it easily becomes silly-looking.
Not to mention that having grown up at different times, many older people's sense of a cool, youthful look is quite off. I'm not saying I'm any better, but a surprisingly high proportion of adults have their 80's or 90's or whatever look in mind and still think it looked okay. Well, I say that, but in 2020, my notion of "stylish" might become awful too.