We definitely have gated communities and some are over 55 developments. The way they stay in compliance with fair housing laws is that 20% of the homes have to be open to people of any age.
So if some young couple with young children want to live there, they can. But you rarely, if ever see that happen. What parents would want to raise their children in a community where the majority of people that live there are senior citizens?? I have worked with plenty of clients that liked a community that is 55 or older, and they could have been able to buy in there. But I've never had anyone that wanted me to even show them a home in one of these communities. But, believe it or not, some young families do buy homes in 55 or older developments. They liked the home so much that they didn't care about all the seniors that live there. Different strokes for different folks, I guess.
As far as what the home owner can do to his/her property in a gated community regarding improvements, even though they do own the land, they still need to have any improvements of any nature approved by the HOA. There are approved colors of paint that have to be adhered to if a resident wants to repaint the house for instance. I have seen situations where the HOA approved a color of paint that wasn't on the list, so there can be some flexibility there. As long as it's a tasteful color, that is close to an approved color, the HOA will let them do it.
Personally, I could NEVER live in a development that had an HOA and maintenance fees. I don't want to be told by some committee what I can, or can't do to my property. But A LOT of people do it. We have gated communities all over the place. And they all fill up with residents. In most cases the lots are all sold before the builder get's finished with all the homes!!!!