Do you have a senior citizen discount and how much? What is the cost to get in?

$8 per person

Major Footnote: Look into the Year Pass and Park Passport **ESPECIALLY if you're into the outdoors throughout the State. Very good deals for both Pass & Passport pending on what your needs are. Passports apply to Seniors, The Disabled, and Military specifically. Here's the page so you can look into all "pass" types 😁 https://tpwd.texas.gov/state-parks/park-information/passes/park-passes

https://tpwd.texas.gov/state-parks/garner

$8 a person 13 years old and younger get in free