Learning new faces: at what age does this ability peak?

Does it peak at age 11?   65?   4?   19?   31? 

Researchers at Harvard and Dartmouth, in a study published earlier this year, found that the mental ability to recognize new faces peaks at age 31 – far later than many would suspect, according to the study’s authors.  The study set out to disprove a common notion that cognitive abilities peak in the early twenties. 
Gathering data from over 60,000 participants, the study traced the ability to learn new faces from pre-adolescence through middle age and, in three separate experiments, found that face-learning ability improves until just after age 30, even though other related cognitive abilities (name recognition and inverted face recognition, which both peaked in the early 20s), peaked earlier. 

The study’s authors said that their data “provide the first behavioral evidence for late maturation of face processing and the dissociation of face recognition from other abilities over time”, adding that this “demonstrates that studies on adult age development can provide insight into the organization and development of cognitive systems.”  

The study was co-authored by Laura T. Germinea (Harvard), Bradley Duchaineb (Dartmouth) and Ken Nakayamaa (Harvard).