It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

Decode below three cipher riddles:

26 L of the A
7 D of the W
1000 Y in a M

Can it be possible to build a house that has all its four walls facing towards the South?

I go up and I go down.
I go up towards the beautiful sky and down toward the green ground.
I am present tense.
I am past tense too
Children love me.

Who Am I?

Can you divide the below-given shape into four equal and identical pieces?

When 99 is considered higher than 100?

Nodes are shown below and you need to connect them based on the following rule: Every node can be connected to the number of nodes inside them, i.e. the first node there is a value of 1 which indicates that the first node can connect to exactly one node only.Can you do it?

John: "Hi Teacher, What is your favourite movie ?".
Chemistry Teacher: "Indium Cerium Platinum Iodine Oxygen Nitrogen".
Ten seconds later... John replied I got it.

Do you?

As easy as you can get into me, it is as hard to get out of me.

Do you know what I am?

Many have heard it, but nobody has ever seen it, and it will not speak back until spoken to. What is it?