If you have a stock portfolio and or retirement accounts, most brokerages will allow you to borrow up to 40% of the portfolio's market value. 

So, they don’t have health insurance, savings, retirement, etc.  

Isn't Buckeye a retirement community?

Over time I'd like to purchase more properties in other beach areas where I might want to retire at some point. 

I'm 23 years old and plan to use real estate for my retirement, but that's in the distant future.My question is whether it's better to pay off the mortgage as quickly as possible or to buy a rental property as soon as possible.My thoughts are that if I pay off my home, I'll have security and more money each month to invest, as I won't have to make mortgage or rent payments.

Since you are looking for passive income from a rental to aid in your income once you hit FIRE & retire, I'd focus on building a portfolio that begins to build on that cash flow to replace your W-2 salary. 

What do fire people do if they are not sure where they want to retire in 10-20 yrs?

What about the retiring persons, our Seniors who are arguably the #1 segment getting devastated by housing cost's today, those on fixed incomes?

However I am looking for long term cash flow and appreciation that I can still manage during retirement someday.

Or he might just retire and spend a lot more time with his young kids.