It is never too late to begin investing! I think the answer in your situation is a big, fat "It Depends". Do you have other debts that need to be paid off? Do you have other savings (emergency fund)? Where are you going to live now that your house and land are being turned into a bridge? What are your priorities? What does your retirement fund look like? I'd recommend using some of the financial planning assessment tools that USAA has on their website as well as giving them a call and talking to one of their financial advisors. You really have to look at this holistically.
That said, when you are ready to start investing, I can't recommend Vanguard index funds highly enough. It is really important to look for LOW fees for your investments. A good place for beginners would be something like a Target Date retirement fund or a mix of Total Market Index (VTSMX) and Total Bond Fund (VBTLX). Good luck!
Congratulations on paying off your mortgage!! and I must agree with ysette9, it is never to late to start investing. We have a financial advice forum where CERTIFIED FINANCIAL PLANNERS answer questions from members. You can post your question there, or contact our team of Financial Advisors here at USAAat 800-771-9960.
I found a few Q&A that are similar to your, if you care to browse through them: