simple words:

grey: hair, eyes, skins->lustreless, dull

full of sleep: weariness, peace, proximity to death 

slow, soft, shadows: a sense of stupor(恍惚)

the bitter aspects of life & the ravages of time

pilgrim soul: moving through life towards the final significance of death and salvation

fuddle 困惑，糊涂.

glowing 发光的，鲜艳的

~when you are old~

1.When you are old and grey and full of sleep

---grey:lustreless,dull

---full of sleep: weariness;peace;proximity to death

2.And slowly read, and dream of the soft look. Youe eyes had once,and of their shadows deep.

---slow,soft,shadow:a sense of stupor

---shadows deep:a sense of the unknown and the mysterious,perhaps implying the calm retained by a person who has not experienced the bitter aspects of life or the ravages of time=innocence

3.pilgrim soul:journeying soul--searching for a place of devotion, moving through life towards the final significance of death and salvation.

4.and paced upon the moutains overhead, and hid his face amid a crowd of stars:suggests Yeat's romantic heartbreak, disturbed and fuddled, yet attaining the magnitude of the universe in the his feelings.