“O me, this sight of death is a bell That warns my old age to a sepulcher.”-What does sepulcher mean in this quote in Act 5 Scene 3

Lady Capulet utters these words and is often characterized
as one of the more vain players on this stage.

What she
means with these words as she casts first glance on her dead daughter's corpse is that
to see a child of hers already laid to rest in a tomb makes her feel old. Not only that,
but also to have lost a child will continue to age her with grey hairs and wrinkles as
stress and sorrow always do.

This word sepulcher means to
bury. I think she is noting that since she is burying her daughter, her time might not
be that far off.