The difference between Senior and Young

When used as nouns, senior means an old person, whereas young means people who are young.

When used as adjectives, senior means older, whereas young means in the early part of growth or life.

Young is also verb with the meaning: to become or seem to become younger.

check bellow for the other definitions of Senior and Young

Senior as an adjective:

Older; superior

Examples:

"senior citizen"
Senior as an adjective:

Higher in rank, dignity, or office.

Examples:

"senior member; senior counsel"
Senior as an adjective (US):

Of or pertaining to a student's final academic year at a high school (twelfth grade) or university.

Senior as a noun (mostly, US):

An old person.
Senior as a noun:

Someone older than someone else (with possessive).

Examples:

"He was four years her senior."
Senior as a noun:

Someone seen as deserving respect or reverence because of their age.
Senior as a noun (obsolete, Biblical):

An elder or presbyter in the early Church.
Senior as a noun:

Somebody who is higher in rank, dignity, or office.
Senior as a noun (US):

A final-year student at a high school or university.

Young as an adjective:

In the early part of growth or life; born not long ago.

Examples:

"a lamb is a young sheep; these picture books are for young readers"
Young as an adjective:

At an early stage of existence or development; having recently come into existence.

Examples:

"the age of space travel is still young; a young business"
Young as an adjective:

(Not) advanced in age; (far towards or) at a specified stage of existence or age.

Examples:

"How young is your dog? Her grandmother turned 70 years young last month."
Young as an adjective:

Junior (of two related people with the same name).
Young as an adjective:

(of a decade of life) Early.
Young as an adjective:

Youthful; having the look or qualities of a young person.

Examples:

"My grandmother is a very active woman and is quite young for her age."
Young as an adjective:

Of or belonging to the early part of life.

Examples:

"The cynical world soon shattered my young dreams."
Young as an adjective (obsolete):

Having little experience; inexperienced; unpracticed; ignorant; weak.

Young as a noun:

People who are young; young people, collectively; youth.

Examples:

"The young of today are well-educated."
Young as a noun:

Young or immature offspring (especially of an animal).

Examples:

"The lion caught a gnu to feed its young."

"The lion's young are curious."
Young as a noun (rare, possibly, nonstandard):

An individual offspring; a single recently born or hatched organism.

Young as a verb (informal, or, demography):

To become or seem to become younger.
Young as a verb (informal, or, demography):

To cause to appear younger.
Young as a verb (geology):

To exhibit younging.