Younger and older does not meet.
But big and small does meet.
Tall and short does not meet.
Breadth does but length never meets...
Who am I?
hehehe the answer is:
Lips. Read the words and you will figure it out
(Your lips touch when you say big and small, and Breath)
The letter B?
"Younger and older" doesn't contain it, "big and small" does, "tall and short" doesn't, "breadth" does at the beginning, "length" doesn't.