Fraunces Tavern is open for Saturday lunch. You can't get much more New York than "New York's Premier Historic Dining Experience" (per their website http://www.frauncestavern.com/)

I haven't eaten there in 20+ years, maybe someone else will chime in with a more recent food update.

GoTravel, I don't think Grammercy Tavern would keep the bar open if they don't serve in the main dining room. I looked at a website (or maybe OpenTable) and saw their hours for Saturday were evening only.

I have eaten at Gramercy Tavern on Saturday afternoons in the tavern room. Great choice. Definitely open all day from lunch on, at least when I went. If you go late for lunch but early for dinner, there is a good chance of getting in without waiting. No reservations accepted. If you do have to wait, you can sit at the bar.

I had lunch at Fraunces a few Saturdays ago. Decent pub grub, basically. Lots of tourists.

Central Park's Loeb Boathouse is the best choice for Grandma's 80th birthday lunch, in my opinion.

I stand corrected about Gramercy Tavern. I see they do keep the bar open on both Saturday AND Sunday, even when they only serve dinner in the main dining room. But I'm not so sure sitting in the tavern is so great for this occassion. Frankly I'd think Grandma wouldn't be that impressed with the decor or bare tables and chairs set up, while the prices are pretty high if you don't really appreciate the quality of the food. (Don't get me wrong here, I LOVE IT, but I'm thinking my 85 year old mother as being just like Grandma -- a nice tablecloth will impress her more than the quality of the arugula!)

Ok...another option. We'll start with the same Boathouse brunch but afterwards have coffee and desert at Cafe Sabarsky in the Neue Galerie (1048 Fifth Ave. at 86th St.) Very pretty and very good pastries -- something different.

I just had a fabulous lunch at Bouley's.
Wonderful atmosphere...fabulous food. There are two prix fixe lunch menus...$34 or $45.
Check it out.......
www.bouleyrestaurants.com

I can't wait to go back!!