I don't think anything will make everyone universally look old. Surely it depends how old you already look 
I think it's a bit dated, I know on mumsnet and often real life a trench is a 'classic' but i rarely see anybody in one and also think they're hard to pull off, you have to dress to wear it, not just put it on over your existing outfit, IMO.
My DM often wears a wide lapel coat very similar to that(aged 70) and it suits her, but she is a very prim and mature dresser.
Have you got the coat and are worried OP? I think it's fine?