It's not an idiom. It's just a sentence -- to be young again means that you are once more younger in age. This can be literally -- like in a Science Fiction time travel story -- or it can be figurative -- like your mind is young again.
It is not an idiom, it means your nose is itching.
Young blood is used to describe up-and-coming young people.
idiom means expression like a page in a book
A spring chicken is the farmer's term for one born in the latest spring. This idiom is saying you're not very young.
Simply its mean a bully.
"Now and again" is the same as once in awhile.
This is the equivalent of our American idiom: If you fail, try try again.
It is an idiom meaning that someone who had stopped drinking alcohol has slipped up and started drinking again.
It means that whatever "they" are makes them feel young again.
It's not really an idiom. It means "what are you thinking about."
RFP is not an idiom. It's an abbreviation.
It is not an idiom, it means your nose is itching.
Young blood is used to describe up-and-coming young people.
It means "do you understand" in an aggressive and standoffish manner. As in "If you show your face here ever again, you will cease to exist... you dig it!"
idiom means expression like a page in a book
It's not an idiom. It means the tip of your nostril.
"Sieve" is not an idiom. See the related link.