How old is the BlackBerry 8703e?

It was released in November of 2006, so it's already 10 years old.

Can I retrieve old messages from a BlackBerry 8703e?

If by old you mean those that were already deleted, there is no way you can recover them unless you have a recent backup of your BlackBerry which included the messages. If it's really important and you need to see those messages, you can get service from companies offering data retrieval.