Replace value based on a conditional in R

I have a df with some age variable, and I would like to padronize it.

    DEATH       CITY    BIRTH    AGE      SEX
> 1 5092017     Acre    3031997   20    MASCULINO
> 2 11022017    Acre    9022017   202   MASCULINO
> 3 11022017    Acre    13071933  83    FEMININO
> 4 11022017    Acre    6022002   15    MASCULINO
> 5 11022017    Acre    2061966   50    FEMININO
> 6 11022017    Acre    28121946  70    FEMININO
> 7 10022017    Acre    4121955   61    MASCULINO
> 8 10022017    Acre    3101943   73    FEMININO
> 9 10022017    Acre    6022017   20    MASCULINO
> 10 9022017    Acre    14012017  226   FEMININO
> 11 9022017    Acre    20071931  85    FEMININO

These lines with 3 characthers represents months (3), days (2) and hours (1) of life, and I want to change it values to 0, as they not completed 1 year old.

I tried to use a if conditional, but it doesn't work...

if((nchar(DO_concatenated$IDADE) == 3)&(funcaoidade(DO_concatenated$IDADE) <=3)){
  DO_concatenated$IDADE <- 0))
  }

"funcaoidade" its a function that i've created to look only the first character of these numbers

 funcaoidade = function(x){
  substr(x, start = 1, stop = 1)
}

As I'm a begginer at R programming, I beg for your help hahaha What Am I doing wrong? Thanks in advance