Get #ERROR! and #NAME? in cell sheet when I use the .setFormula () in Google Apps Script

I'm trying to include a function in cells in a column, based on the value of the cell in the same row in the next column and the value in a fixed cell.

I have created my code in GAS that you can see here:

function enviar_datos_formulario_anadir_mascota_a_bd_fichas() {

  var libro = SpreadsheetApp.getActiveSpreadsheet();
  var hojaOrigen = libro.getSheetByName("Añadir ficha");
  var hojaDestino = libro.getSheetByName("BD Fichas");

  var row = hojaDestino.getLastRow() + 1;

  var fechaHoy = hojaDestino.getRange("H6").setFormula("=TODAY()");
  var fechaNacimiento = hojaDestino.getRange(row, 9); 
  var edad = hojaDestino.getRange(row, 8);

 edad.setFormula('=IF(ISBLANK(\'fechaNacimiento\')=FALSE;DATEDIF(\'fechaNacimiento\';\'fechaHoy\';"Y");"")');

}

I have also tried with:

edad.setFormula('=IF(ISBLANK('+fechaNacimiento+')=FALSE;DATEDIF('+fechaNacimiento+';'+fechaHoy+';"Y");"")');

And also with:

edad.setFormula('=IF(ISBLANK(\"fechaNacimiento\")=FALSE;DATEDIF(\"fechaNacimiento\";\"fechaHoy\";"Y");"")');

For whatever reason, I can't get it to work. It throws me the #ERROR! or #NAME? notice. I attach screenshots below:

Could someone tell me what the problem really is?

Thank you in advance