Very Easy Answer --
Add a 5 or 10 second bonus to whatever speed(s) you play. And PRACTICE, and STUDY, all phases of the game.Game in 3/5 up to Game in 30/10 will give you all the practice you need.
Instead of Game in @5 hours, you should (perhaps) STUDY chess instead.
Don't be surprised if you Blitz strength is 200-300 points weaker than you OTB strength.
It depends on age too. Your reflexes slow down, later in life.
I don't really have many resources to "study" chess. Also, here it is nearly impossible to get a seek with a time control of 30|0+ accepted here.
Btw, it certainly doesn't depend on my age, I'm under 14. :P
Zborg's advice amounts to "play slower chess".