Why does she have to ''feel that age''? Age is a construct of human society anyway, born of a bunch of factors including passing through certain life stages/having certain experiences, as well as biological age. If Diana doesn't age physically and if Amazons don't go through the same life stages or experiences a 'normal' human being would likely go through, then why would her concept of age be the same as ours? It becomes immaterial if she's 20 or 40 or 500 or 2000...
Exactly!
Gal Gadot's Diana looks like a 30-something and is canonically thousands of years old (the exact number is mentioned in Snyder's JL, I don't remember it right now). It doesn't stop her from being a naive ''fish out of water'' when she first shows up on Man's World. And she's probably had more unique life experiences in the nearly 70 years between the first film and WW'84 than she had for the thousands for years before that.