Return start and end ages for id
from when it first appears to when it splits
Examples
data(mammals)
# mammal_age <- getAge(mammals) # ~166.2, needs to be performed when tree is not up-to-date
getSpnAge(mammals, id = "Homo_sapiens", tree_age = 166.2)
#> spn start end
#> 1 Homo_sapiens 9.7 0