Nevertheless . . . here is one way you can deal with the issue you had:
1. Create a query using the City and Age fields from your table.
2. In a new field in your query put this:
Code:
Age_Group: IIf([Age]<4,"0 - 3",IIf([Age]>7,"8 - 12","4 - 7"))
This will put each of your Age values into one of the three age-groups.
I haven't considered any age-groups other than what you mentioned.
The highest Age I put in my test table was 12.
3. Run the query to see that it did what you expected.
4. Click the Make Table button at the top.
5. Save and run the query - it will create a new Table - with an Age-Group column. You can open it to check it is correct.
6. Click Create -> Query Wizard -> Crosstab Query Wizard.
7. Follow the steps selecting City for the 'Row' and Age_Group for the 'Column'.
That should give you what you need.
Let me know if that helps!!