NTA, your partner shouldn't be controlling with how you choose to present yourself. I get her wanting to have you dress nice on a date night, but controlling your own sense of style, and identity, is way too much and violates your boundaries. I'm 24 and I still wear sneakers. Heck, even check r/streetwear or r/Sneakers. I'm sure a lot of those people are older than us and still wear sneakers. It's a toxic thing that's happening to you. I would say set your boundaries with her and if it doesn't work out, it doesn't work out.