Whats the deal with 55+ Communities?!?!?!

[Jabari Brooks]

I'm noticing some really well kept homes priced what seems to be low in "Nice and quiet 55+ gated communities".  What's the deal here?  

Are these neighborhoods black eyes for investors, causing the low list price to entice a sale?  Are there certain restrictions associated with purchasing properties in these neighborhoods?  Do they prevent a certain type of renter from being interested thereby causing delays in getting filled?  

Do you have any experience with these communities good or bad that may help shed some light?