[R] Specifying xlevels in effects library

[David J. Netherway]

library(effects)
mod <- lm(Measurement ~ Age + Sex, data=d)
e <-effect("Sex",mod)
 
The effect is evaluated at the mean age.
 
 > e
Sex effect
Sex
       F        M  
43.33083 44.48531  
 >
 > e$model.matrix
   (Intercept)      Age SexM
1            1 130.5859    0
23           1 130.5859    1
 
To evaluate the effect at Age=120 I tried:
e <-effect("Sex",mod,xlevels=list(Age=c(120)))
but the effect was still evaluated at 130.5859.
 
Is this an incorrect usage of xlevels?

Thanks, David