There is some correlation between the age of the other girls (pink circles) he played with and how high the Fun Score is. In general, the older the girl he played with, the higher the Fun Score on that play date. For example, AA (girl) at age 7 scored a Fun Score of 10, whereas LK (girl) at age 2 scored a Fun Score of only 4.5 (see the pink best fit line). He doesn't seem to have much interactions with a 3 month old MC and the Fun Score is nearly 0.
The same is true when my son plays with other boys, though the correlation isn't as strong (and also, there is lack of data points). For example, CK and CK2 (who are close in age) only wanted to play with each other and ignored my son most of the time despite repeated attempts of getting them to play together. Then there is an outlier (EP) who was older and score a high Fun Score of 8. He was the most friendly and well-socialized boy of all the boys we've met to date and scored nearly as high as AA (girl).
Subjectively, I noticed that with my son, the boy-girl interactions tend to be a bit more constructive especially with older girls where she would often help or guide my son to do things. On the other hand, boy-boy interactions tend to be a bit more violent and more destructive, where they often throw things or destroy stuff (pull off legos, kicking block castle down, etc). Many times, they just ignored each other or simply co-played (defined as playing the same toys, but not interacting directly with each other via verbal or visual communications).
Note that my observation is subjective and that data points are sparse and self selected. Most importantly, my observations are mostly relevant for a 2.5 year old boy-- my own son. If you have [anti] anecdotal tales like "This report is flawed, I know this one particular case where x year girl/boy would score y", then feel free to email me personally. On the other hand if you have more data points (10+) that you'd like to share, then I'd really really really love to hear from you!