Italian for 50th Birthday Celebration
I think Del Posto is a great place for large group dining, and the decor and service will be something that a 50th year old appreciates. The inside is a bit dim-light and very spacious. The food is rustic yet serves in upscale style (small portion on big white decorative ceramic plates). Everytime I dine there I see families sitting in round table. Food, especially pasta which is Batali's specialty, is fantastic. In general I think Del Posto is a good choice for group celebration.
If you prefer a more cozy restaurant, then Hearth will be a good choice. The food there is slight more contemporary, yet simple and comforting. The service is impeccable and the staff is very friendly. It is great for family dinners, and more causal than Del Posto.
Hope you have a wonderful 50th Birthday party!