page speed test with google – result is not good

Hi,
I only using GD plug in and GD booster plugin and I am using geo starter theme.
There are only 900 records in my database.

But google page speed result is red 60/100 only.

Attached is the result and recommendation from google page speed tester.

After reading GD booster add on , I thought GD directory will have best performance with its own cache solution.

It is turn out that it is not true for mobile as desktop page speed achieves 83/100 although it should achieve min 90/100.

Any ideal how to speedup especially mobile.

Rgds,
yc