How close are we to DIY viruses?

If I was a teenager interested in biology, and I wanted to maybe build a "harmless" virus just to see if I could do it, how achievable might that be?

I watched computer viruses go from:

researchers -> tinkerers -> vandals -> criminals -> governments

At this point we just assume every computer is compromised, and we carve out enclaves of varying security for whatever risk level we're willing to assume.

I can imagine a future where pandemics happen at the same frequency as school shootings do today. How far away is that?