错误:找到的对象不是一个属性

I'm using the following code:

我使用以下代码:

library (ggplot2)
df=data.frame(score=c(1,3,5,9,7,8,4,1,2,6,1,6,2,1,3,1,3,5,8,4),
              age=c(2,2,2,2,2,2,2,2,2,2,3,3,3,3,3,3,3,3,3,3))  

ggplot(data=df,aes(x=age,y=score))+
     geom_point(position=position_jitter(width=.1),aes(color=age))+
     geom_line(stat = "hline", yintercept = "mean",aes(group=age))+
     stat_summary(geom = "line", fun.y="mean",aes(yend=..y..),width=.5)+
     stat_summary(fun.data="mean_cl_boot",geom="errorbar",width=.5)+
     theme_classic()
libr