Sure! Here are the completed sentences using the double comparative structure:

1. The older James got, the wiser he became.
2. The more modern the city was, the higher the living standard got.
3. The younger the children are, the easier it is for them to remember the lesson.
4. The more expensive the hotel is, the better its services are.
5. The dustier the road is, the itchier my eyes get.

If you need further assistance, feel free to ask!