paternal, parental

Paternal or paternal describes something associated with or belonging to a  father--
The colonel addressed his troops in a paternal way.
The inmates sometimes resented the warden's paternal attitude.

Parental or parental describes something associated with or belonging to a mother, a father, or both--
Make sure that children have parental guidance when watching this program.
Make sure that our clients have a clear understanding of their parental rights and obligations.

Now that you know that, you can say--
"The old man showed a paternal feeling for the young couple struggling with their new parental status."