Given your wife’s preferences, I’m inclined to suggest B & O Brasserie, .4 miles down Charles Street. It’s relatively fancy and solidly “upscale mainstream American”.

The only thing is that their hours on Sundays are 8-12, then opens again at 5. You would be looking more at late breakfast/early brunch.

It’s a great spot — I’ve celebrated my birthday there in years past.

Otherwise, CIVIL, EDR (Eat Drink Relax), and some places in Mt Vernon Marketplace might work. My only reservation with Mt Vernon Marketplace is that the options are quite diverse in terms of cuisine styles (off the top of my head, Asian dumplings, tacos, Korean/fusion, ramen). There is a great oyster place, a good burger place, and a fish place (Fishnet). All are fun, but they seem less “birthdayish” to me.

If you switch over to having dinner, a number of other options open up, including the classic Sotto Sopra (Italian) down the street between Walters and B & O Brasserie (right near the Cathedral). Sammy’s Trattoria also opens at 5, and is the opposite direction (north).