When a child has disobeyed their parents as a youth but then when parents reach old age and parents are happy with their child, does this mean that child's repentance has been accepted in regards to obedience to parents in their old age? Regardless if tauba has been accepted or not, if parents are happy when their child towards the end of their life, does this mean that the child has made an attempt to serve his/her parents to the best of his/her ability?

All perfect praise be to Allaah, the Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

If this young man had sincerely repented from his undutifulness to his parents while fulfilling the conditions of repentance that are mentioned in Fatwa 86527, then his repentance is accepted, Allaah willing, as Allaah promised to accept the repentance of those who had repented and Allaah does not break His Promise, but most people do not know.

The scholars stated that among the signs of the acceptance of repentance is that the state of the person becomes better after it [i.e. he would be enabled to perform good deeds and stay away from acts of disobedience].

Therefore, if this young man has become kind and dutiful to his parents and has gained their pleasure, then this is a good sign that may suggest the acceptance of his repentance.

Hence, he should be steadfast on this, and thank Allaah for this blessing and for the fact that had it not been for the favor of Allaah on him, he might have died while performing a bad deed.

For more benefit on the virtues of being kind and dutiful to one's parents and the seriousness of undutifulness to them, please refer to Fataawa 87019 and 85041.

We did not understand the last part of your question, but we say that pleasing the parents after having been undutiful and disobedient to them is important and it is among the requirements of a sincere repentance, but other requirements should also be met.

Allaah Knows best.