Car wont start. When the key in ignition,I hear only click.

What is your question?

I did not use the car for 5 days. Just had my A service done 10 days ago. Today, it wont start. All internal and external lights go on, including radio when key is in ignition, but no sound from engine, only light click sound. This never happened before. It still has the original battery (5.5 years old). I did not try to jump it yet but some friends suggest it might be the starter issue. I do not want to buy a new battery until I figure out what is the main issue. Thanks for all suggestions and help.