I found it interesting that there are a large number of counties where the over 65 year olds are a relatively small percentage of the eligible voters. While some of these are already blue the others could turn blue if enough younger voters actually vote, at least in counties where the young aren't totally brainwashed too.
Brazos 11.2%, Travis 12.3%, Coryell 13.0%, Denton 13.1%, Gaines 13.5%, Garza 13.5%, Loving 13.6%, Hays 13.8%, Webb 13.9%, Harris 13.9%, Ector 14.1%, Dallas 14.3%, Midland 14.5%, Collin 14.6%, Bell 14.7%, Fort Bend 14.7%, Tarrant 15.0%, Walker 15.0%, Andrews 15.2%, Bee 15.4%, Moore 15.5%, Reeves 15.5%, Waller 15.6%, Brazoria 15.7%, Chambers 15.8%, Frio 15.9%, Reagan 15.9%, Bexar 16.0%, Lubbock 16.0%, Williamson 16.1%, Ochiltree 16.1%, Hidalgo 16.2%, Howard 16.4%, Dallam 16.5%, El Paso 16.5%, Kaufman 16.5%, Potter 16.8%, Martin 16.8%, Maverick 16.9%, Starr 16.9%, Rockwall 17.0%, Crane 17.0%, La Salle 17.0%, Kleberg 17.1%, Ellis 17.3%, Liberty 17.3%, Yoakum 17.4%, Winkler 17.5%, Montgomery 17.5%, Pecos 17.5%, Erath 17.6%, Karnes 17.9%,
There are also some counties with a lot of older folks 65+ where Republican support is dying off.
Llano 42.1%, Sabine 37.9%, Motley 36.7%, Gillespie 36.6%, Menard 36.5%, Mason 36.2%, Jeff Davis 36.1%, Terrell 36.0%, Kimble 35.6%, Edwards 35.1%, Real 34.7%, Throckmorton 34.5%, Mills 34.5%, Kerr 34.0%, Foard 33.7%, Coke 33.7%, Wood 33.6%, Aransas 33.6%, Stonewall 33.5%, Kent 33.2%, Trinity 32.7%, Hamilton 32.0%, Cottle 31.9%, Bandera 31.8%, Concho 31.8%, San Augustine 31.7%, Baylor 31.6%, Briscoe 31.6%, Coleman 31.2%, Fayette 31.1%, Hood 31.1%, Marion 31.1%, Comanche 31.1%, Bosque 31.0%, Leon 31.0%, Presidio 30.9%, Hall 30.7%, Fisher 30.4%, Lavaca 30.3%, Red River 30.3%, Rains 30.3%, Donley 30.2%, Borden 30.0%
Data from the Texas Association of Counties