depends how you are for your age , I know people quite young , that act way beyond their age ... no-one can tell you an age cut - off other than yourself how you feel ..
I'm 25 and I wear trainers mainly runners ( ZX, Asics, NB , Puma) if it suite your style wear it ....simple. Nice pair of runners , raw denim and quality sweatshirt , comfy easy outfit imo I wear shoes , superga, boots and top-siders so not only this or that haha
But If will see 35+ man walking down in adidas , si , hackett cap it's a bit .....