Many 55+ RV resorts are somewhat flexible with the policy. Despite being millennials, there were multiple times when we were able to score reservations at age-restricted RV resorts.
Many people in these communities would rather not camp with many kids around. Not having children made it easy for the management to be flexible with us.
Their biggest concern is typically not disrupting other guests who meet the age requirement. Anything you can do to ease their worries, including not having pets, can help.
Whether you agree with the rules or not, you must follow them to stay in these resorts. If not, management may change their mind about making a policy exception for you.