People read it in different ways, I guess, I would never take it (certainly not in context) as "I love this woman, but gawd damn she old AF and I can see the wrinkles!" When I first saw it while playing that ending, I read it as she is getting older and she's not overly happy about it.
She is clearly conscious of her age at this point, or at least the age difference between her and both MC and little Shelby, and she looks tired too - probably not helped by running around after a toddler and still having an energetic sex life too! She didn't want to celebrate her birthday, she just wanted to ignore it, pretty much.
Also, just to throw another spanner in there, it's the narrator saying it, not MC - "your wife" as opposed to "my wife", so it's not (necessarily) saying "I think my wife looks old and wrinkly (but still beautiful)." Even then, the text literally still says she remains beautiful.