Has Cech Petr-ed out??

I like Cech, but this season he has been pretty poor.

As of now (the international break), he has 4 Premier League clean sheets, which is not that far behind Courtois, Lloris, or de Gea as other top six team keepers.

He, of course, holds the Premier League all-time clean sheet record, and the joint record holder of the Golden Glove award (for the most clean sheets per season).
But are we seeing the end of what has been a great goalkeeper?
In 17/18, he has had some good games, but mixed with some bad errors:

Everton (A)

Monreal possibly should share some culpability here. But then he could have hoofed it when receiving the back pass.

Swansea (H)

The Swansea attack should have been closed down, but Cech was slow to come out and close the player down.

These instances were not that costly, granted, since we won both games. But the Cech of Chelsea and his first season for us seemingly is not as grand.
So what is causing this decline?
Is it his age? Keepers have always aged better than outfield players. Many of the greats in history, from Zubizerrata, Zenga, Buffon, Shilton, Banks, Southall, even Schmeichel and Seaman, were capable keepers until their late 30s. Cech is 36, and has a few years left yet at the top level. So age is not the principal factor.
Is it the alleged “bad coaching” from Mr. Payton? Possibly, if true. Though Cech is a seasoned enough keeper to have learnt some skills over the years, and may not even need extensive coaching. There has to be some innate talent, along with being guided, or coached. It’s like if we signed Ronaldo and Messi, and even with poor tactics/preparation, both would excel since they hold innate talent. Messi was born skilled, whilst Ronaldo is highly driven and often self-trains, as it were. To be successful in any avenue in life requires some natural skill, and cannot solely be imparted from others.
Is it the defence? Man for man, Arsenal’s defence as of this season isn’t’ that worse than Chelsea’s in 2014/15. Even now, Cahill isn’t that good, compared to Koscielny or Mustafi. This should in some ways be a boon, especially to a seasoned shop-stopper like Cech. He would thus be the hero more times than not, and prove his credentials as being a top keeper.
Is it the overall malaise at the club causing this? Possibly. We all need sound environments to work in, no matter how experienced we are.

I cannot put my finger on what is causing his poor form, though it is a worry.
He is one of the best keepers in England in both Premier League history, and of all-time in England, and our best keeper since Lehmann (possibly Seaman). It is sad to see him decline in this manner. However, there is always room for improvement, no matter how good one is, and let’s hope he can resume some form in the coming games.

That said, he did make some telling saves in the recent City game, which certainly limited the score. However, this needs to be done without any mistakes attached.