You see the parents of a baby obviously less than one year old. You want to ask how old the baby is. Would it be natural or ridiculous to ask "Cuantos años tiene?" In other words, would the literal sense of the words suggest the answer "none," or would everyone simply understand the question to mean "How old is he", without distraction?
What about changing "años" to "meses" or "semanas" — is that natural or ridiculous?