Are elementary particles as old as the universe? Lets take quarks for example. Are the quarks - that constitute the universe - as old as the universe? Or are particles always created? Or were they all created when the universe was born?
 A: 
Are elementary particles as old as the universe?

Some of them are and some of them aren’t.
The quarks and electrons in most atoms have been around since the Big Bang. The photons of the cosmic microwave background have been traveling across the universe for almost 14 billion years.
On the other hand, every kind of elementary particle can be created and destroyed. It is particularly easy to create massless particles because they can have arbitrarily small amounts of energy. A radio antenna, for example, creates scads of low-energy photons. The Sun creates enormous numbers of photons and neutrinos.
It takes more energy to create particles with mass, because their minimum energy is $mc^2$. But we do this all the time in accelerators. A high energy photon passing by an atom can pair-create an electron and a positron. Two colliding protons can create multiple quark-antiquark pairs. Or a Higgs boson. Etc. Feynman diagrams represent particles interacting and sometimes appearing, disappearing, or turning into a different kind of particle.
Relativistic quantum field theory was designed with particle creation and destruction as a core feature. A quantum field is a field of operators that create and destroy particles! This is very different from, say, the non-relativistic quantum mechanics of the Schrodinger equation.
In conclusion, some elementary particles are very old, and others are brand new.
