What is the test for making a voluntary confession in a murder case?

'This, then, is the general rule: a minor has the capacity to make a voluntary confession, even of capital offenses, without the presence or consent of counsel or other responsible adult, and the admissibility of such a confession depends not on his age alone but on a combination of that factor with such other circumstances as his intelligence, education, experience, and ability to comprehend the meaning and effect of his statement. (See cases collected in Note, 87 A.L.R.2d 624.) Applying the 'totality of circumstances' test of Gallegos [Gallegos v. Colorado, 370 U.S. 49, 82 S.Ct. 1209, 8 L.E.2d 325] such confessions have been held admissible when made by a minor of the age of fourteen, fifteen, sixteen, seventeen, eighteen, nineteen, or twenty. As the court concluded in State v. Carder (Ohio 1965) supra, 3 Ohio App.2d 381, 210 N.E.2d 714, 719, after reviewing the facts surrounding the murder confession of a 16-year-old youth. 'Under this 'totality of circumstances,' for his statements to be inadmissible we would have to told that any self-incrimination of a person under 18 years old is involuntary unless his parents or his attorney are present. We would also have to hold that such minor is not mature enough to make a voluntary confession or waive the presence of his parents or his lawyer during any conversation with the police. This is not the law.' (Italics added.)