My website has score of 89% on GTmatrix. It is showing links of images in which expiration is not specified. How to specify expiration on images?
How To Speed Up WordPress
Themes have lots to do with speed, as well as pictures.
I find staying pretty close to the default themes takes care of many speed issues. WordPress is great, but it can easily get bogged down. Check your plugins, check your image sizes.
fixmywp.com, putting this in your .htaccess will set expiration.