Distribution of firm sizes and firm age What are public sources for US firm/plant sizes, in order to characterize the firm size distribution? And what are stylized facts about the firm size distribution: What does it approximate to? 

Somewhat related: What about the firm age distribution? That is, the distribution of firms given their age. I understand the latter is a soft concept in the data, but are there first-order approximations for age, and how does its distribution look?
Compustat Annual is used in Gabaix and Landier (2008). A famous stylized fact is the power-law distribution (by Gabaix again) of firm sizes. But power-law claims have been criticized as resulting from poor measurement.