What does "in the sere and yellow" mean?

I am currently reading "A Study in Scarlet" by Arthur Conan Doyle. On page 33 is a sentence I don't understand:

Well, if a man can stride four and a-half feet without the smallest effort, he can't be quite in the sere and yellow.

What does "in the sere and yellow" mean?

Note: It seems to be related to this part of Macbeth:

I have liv'd long enough: my way of life
Is fall'n into the sear, the yellow leaf;
And that which should accompany old age,
As honour, love, obedience, troops of friends,
I must not look to have; but, in their stead,
Curses, not loud but deep, mouth-honour, breath,
Which the poor heart would fain deny, and dare not.

It means he has not yet entered the autumn of his life, and is yet fit and hale.

In a comment below, MetaEd writes:

‘Sere and yellow are descriptive of an autumn leaf. Thus “in the sere and yellow” is a metaphor for being near the end of one’s life. In the quoted passage, it is used to mean that he has not yet entered the autumn of his life, and is yet fit and hale.’

As in the Macbeth quote, "in the sere and yellow [leaf]" is a poetic way of saying of advanced years, elderly. I don't know if Shakespeare actually coined it, but he certainly gave it currency.

Sere (also, sear) - dried and withered, carries much the same significance as yellow in this specific metaphoric context. Like autumn leaves, an old person's skin may be yellow and withered.

Here's a typical self-explanatory example - "...he was in the "sear and yellow leaf" of his life."

Metaphor for a withered autumn leaf ... here's another one, in the description of the tattered sails of the Ancient Mariner's ship

"The planks look warped! and see those sails,
How thin they are and sere!
I never saw aught like to them,
Unless perchance it were
Brown skeletons of leaves that lag
My forest-brook along"