Solution:

24 Years

If you were 8 years old 8 years ago, then your current age is 8 + 8 = 16 years old.
After 8 more years pass, your age will be 16 + 8 = 24 years old.

So, you will be 24 years old in 8 years from now.

Solution:

A SINGLE WORD.

Solution:

11

You already knew the answer wasn't 26 letters. That would be too easy.
The letters in the words "the alphabet are 11

Solution:

The third Boy was in a wheelchair so he rolls out of the room instead of walking out.

Solution:

Chilwell can go through as all the person whose name contains even number of letters can go through the door.

This is a classic green glass door riddle.

Solution:

3

Explanation:
If I had 4 eggs -- Its just imagination.
A thief gives me 3 -- I go three eggs.
My farm rooster lays 5 eggs -- A Rooster can't lay eggs.

Solution:

There are 7 people.

Solution:

In a clock.

Solution:

The girl sitting on your lap.

Solution:

The boy in the center. He doesn't have any shadow.