To qualify as a first time buyer you must have not owned your home for the last three years. You may also qualify for the down payment assistance programs that Houston has up to $19,500 and also another program LIFT with an additional $15,000. Some restrictions apply but as a first time buyer specialist, I urge you to check on these programs and other programs available to you. I am a certified TAHS (Texas Affordable Housing Specialist) and can guide you if you need my assistance.
If the buyer has not owned a home within the last 3 years, he is then considered a first-time homebuyer and could apply for any first time homebuyer programs, that he qualifies for. I hope that this helps :)
The definition of a first-time home buyer can be found in the 2008 Economic Recovery Act, which added the definition to section 36. In this legislation the terms that define eligibility for first-time homebuyer status are found within the federal tax code under Section 36(c)(1). It explains that a party must not have had ownership interest in a principal residential property within 3 years before buying a new home. The 3-year term is counted from the date the previous property was purchased, not from the time of actual occupancy. See the link below.
It will really depend on why they need to qualify as a first time home buyer. Certain downpayment assistance programs have different guidelines. Could you elaborate? It seems like your client is trying to buy a new home with a DAP, if so, check with the DAP and ask them directly. The builder or salesperson will only know what they remember. They don't make the final decision.
Each person's situation is somewhat different. I was surprised to find out one of my buyers qualified under a first time buyer program because it had been some time since she owned. Ask a good lender and see what programs you qualify for. It may be that you qualify under a different program even better for you and your situation.