Granted, the Greek term tekna has no age-related limitations. For an example, we find it also in the heart-warming parable of the ‘prodigal son’, when the ‘father’ of the parable uses this term in relation with the eldest son of him (Luk 15:31).
However – biblically - the obligation to obey own parents seems clearly linked with the age maturity of a son/daughter, expecially when it is related with a starting of a new family. In this instance, when a son assumes on himself the responsibility of a family (with or without children), he becomes free from the his parents’ authority. The same happens if a conjectural son reaches a marriageable age, and so he decides to live outside the parental home.
The passage from the parents’ responsibility of a behaviour of a son and the time in which this son assumes his own full responsabilites is well illustrated in the account of the healed born blind one.
We read that, to get some testimonies about the astounding healing of that man, the Jewish religious leaders called as witnesses the parents of the born blind one.
We read (bold is mine): “But the Jews did not believe that he had really been blind and that he had come to see again, until they called the parents of the man who saw again, and asked them, ‘Is this your son, and do you affirm that he was born blind? If so, how is it then that he now can see?’ His parents answered, ‘We know that this is our son, and that he was born blind. But we do not know how it is that he now can see, or who it was that made his eyes to see. Ask him; he is of age; he can speak for himself.’” (Joh 9:18-21, Williams’ NT)
Until some time before those parents did really speak for (or, ‘instead’) their son, assuming on their shoulders the consequences of the behaviour of their son, at the epoch of that questioning the born blind man was ‘of age’, instead. He did must speak for himself, assuming on himself every responsabilities related with his behaviour. His parents were free from exercise authority on their son.
Despite we may have some troubles to fix today an exact amount of years as equivalent to be ‘of age’, the point stands again: when a son arrived to be ‘of age’ – living outside the parental home - he was free from his parent’s authority.
This concept is confirmed also by the other famous parable of the prodigal son we mentioned above (Luk 15:11-32). In it we see how the father did not interfere with the decision of his son to get his share of the property. He did not oblige his son to remain in the paternal home. More probably, according the implied background of this parable, we may imagine that the younger son did inform his father not only about his desire to get part of the property, but also to leave the paternal home to start a new life for himself. Moreover, the parable says nothing about a kind of putting a tail on his son (from the father’s part), to know in what manner he would spend that freshly received capital.
As regards women, in the Biblical times they passed from the parents’ authority to the authority of her husband (1 Cor 11:3).
Another point.
Speaking about the making of a new family, Genesis 2:24 states: “Therefore shall a man leave [ozb] his father and his mother, and shall cleave unto his wife, and they shall be one flesh.” (JPS).
This statement was repeated by the Lord Jesus (Mat 19:5; Mar 10:7-8), as well as the apostle Paul (Eph 5:31). In these NT passages we always find the compound Greek verb καταλειπω, from κατα (an intensive particle) + λειπω (to abandon, to leave [behind], to neglect [as in Act 6:2]). The same Greek verb was used yet by the Greek Septuagint reading of Gen 2:24.
What about the Hebrew verb used in Genesis?
Ozb has the same meaning of the Greek homologous term, plus a little more emphasis on the freedom-from-authority concept. In fact, as a derivative noun we find that the Bible term ozub has the meaning of ‘a not-slave person’ > ‘a freedman’, as we see in Deu 32:36; 1Kin 14:10; 2 Kin 9:8.
Thus, we may safely conclude that both in Hebrew and in Greek language - besides the general meaning of ‘to leave, abandon’ - we may deduce that καταλειπω/ozb both possess an authority-related idea of “to make a clean break with the authority of someone.”
Then, when Gen 2:24 speaks about to ‘leave’ father and mother, it not intend merely that the new couple of newlyweds - from a time on - will live in an independent house, but, in a more pregnant meaning, that the ‘bridegroom’ Genesis speaks about, was ready to leave behind the parental authority he was subjected to, until that moment.
So, the direct answer to your question (“Does a faithful reading of Ephesians 6:1 require adult Christian children to obey their parents?”) is: ‘No’ (except if decide to remain voluntarily subjected to the authority of his father, abandoning not the parental home).
This doesn’t mean that an adult (or ‘of age’) son has right to show disrespect towards his parents (and least of all, that he now has an authority over his parents). The Scriptures (1Tim 5:4) explains us that we are obliged (as a Christian) to give compensation (or, recompense) to our living progenitors (προγονος, ‘parents’, ‘grandfathers’, and other living ancestors). The context (verses 3-16) of this passage included in the ‘compensation’ also the economical care of these ancestors from the sons/grandchildren part.
Last point.
I’m agree enough with Rajesh statement: “If your parents command you to do something that is in accord with God’s righteous standards, then to obey them is to obey God, and we are obliged to obey God no matter what age we are”.
Right, but this point is applicable to every person, not only parents.
For an example, also a young person may offer to more aged peoples some counsels derived from divine wisdom included in the Bible. In these cases, too, we may say, ‘to obey him is to obey God, and we are obliged to obey God no matter what age he is” (compare Qoeleth 9:14-15; Job chapters 32-27).
I hope these notes will be useful for you.