De R a STATA: errores por caracteres en nombres de columna

grepl_dta.R

library(tidyverse)
library(haven)
library(labelled)

#crear data frame
set.seed(22)

dta <- data_frame("edad" = floor(rnorm(6,25,10)), 
                  "sexo.per" = gl(2,1,6, labels = c("f","m")),
                  "grado_academico_a_nivel_nacional_" = rep(c("primaria",
                                                              "secundaria"),
                                                            each=3)) 
#regla
!grepl("^[A-Za-z_]{1}[A-Za-z0-9_]{0,31}$", names(dta))
#fuente:
#https://github.com/tidyverse/haven/blob/master/R/haven.R

#con error
dta %>% write_dta("data/test.dta")