In the Breaking Bad pilot, chemistry teacher Walter White gives this speech:

Chemistry is the study of matter, but I prefer to see it as the study of change.

Now, just think about this.

Electrons, they change their energy levels.

Molecules change their bonds.

Elements, they combine and change into compounds.

Well that's... That's all of life, right?

It's the constant, it's the cycle... It's solution, dissolution, just over and over and over.

It's growth, then decay, then transformation.

It is fascinating, really.

He has just turned 50.

This begins his start of a journey to sociopathy.

He does not turn 51 until the start of season 5.