You may be confusing two completely different property types. 55+ communities are normally condo/villa type arrangements that have HOA guidelines for residents to follow. These physical arrangements do not include larger animals such as horses.
There are residential areas in Florida that do allow horses but normally have a certain number allowed per acre. Acreage is not a realistic consideration with 55+ areas. So your best bet for finding accomodations that will meet your needs is to concentrate on areas that promote horse ownership for their residents.
We would be happy to identify locations in Sarasota County that may meet your needs....but the won't be 55+.