When Can HOA be Formed?

I have lived in my neighborhood for 11 years without an HOA. When I first bought the house in 2005, I was told that there could be an HOA,and there were HOA rules but since it was a new development, the HOA would be developed later when more homes were built. In 2016, one person in the neighborhood decided to initiate the start of the HOA. We were billed an initiation and all the back dues from when we purchased the home. This is located in PA.

1. Is it legal to be billed dues for when there was no HOA?
2. Can the HOA be formed and all homeowners required to join after all these years?
2. I found out the HOA was in a lawsuit. Are the legally required to disclose this information to the homeowners when money from the reserve was used to cover the cost of the suit?

Yep, sounds like you have deed restrictions, CCR, etc which means HOA. There is no "joining" By having the deed restrictions, you are a member of the HOA simply by purchasing the home. As far as the lawsuit? Who knows..... complicated.

I maybe showing my ignorance, but isn't it possible to have deed restrictions without having and HOA?

It definitely is. That's why the legislature passed the MRTA statute years ago. It wasn't targeted specifically at HOA deed restrictions, it was meant to extinguish many old deed restrictions, many of which dated back to the Spanish Land Grants. Those crusty old deed restrictions probably had nothing about any homeowners associations in them.

Having an HOA implies deed restrictions but deed restrictions alone don't necessarily imply an HOA.

OP is long gone.