See this oped in the Austin-American Statesman. A snippet that the authors use to bolster their case to me points in the opposite direction:

A majority of the elderly hold valid Texas driver’s license: 73 percent of the age seventy-nine and 63 percent of 85-and-older population. Most telling is that 93 percent of elderly voters who voted in 2006 in Harris County– the state’s most populous county — hold a valid Texas driver’s license. Even more hold a Texas ID card, utility bill, hunting license, library card — all forms of acceptable identification in HB 218, which passed the Texas House.
Opponents’ concern over disenfranchising the elderly is especially dubious since one bill passed by the House exempts people older than 80 from the identification requirement. If a person does not possess and is unable to procure identification, that person can vote by absentee ballot, a process unchanged by the voter identification bill. The voter identification bill also provides for a free ID card to any registered voter who doesn’t already have one and can’t afford one.
Vote fraud has been well documented. In 2006, the attorney general investigated 59 cases and noted that the highest concentration of voter fraud is in the vote-by-mail process though there have been three instances of alleged illegal voting, which may include circumstances preventable by a voter photo ID law.

(my emphasis)