Is there a past due notice to customer template?
can i generate past due notices for aged invoices
can i generate past due notices for aged invoices

Couple options:
Create and mail statements to customers or
Click on Company and select "prepare letters with envelopes" option for the actual past due letters. You may need to customize them first if you want your company logo displayed.
You have multiple options.
1. you can create an invoice template with verbiage stating that this is an overdue invoice ... or words to that effects.
2. you can use the letters feature within QuickBooks to create a letter to send to your customer to inform them of the overdue invoice and/or invoices
3. you can create a statement from the QB file to combine all outstanding invoices into a single page and send that to the client.
Let me know if this helped and/or if you'd like more information. If none of these are a option I'm sure we can come up with something that will work for you
Alexis Sadler