In this work, we focus on developing touchscreen text-entry interfaces, specifically focusing on finding the optimal touchscreen keyboard interface which can capture variation among the older adults with dyslexia. The major contributions of this work are: (1) development of a design space for text-entry interfaces, (2) design and initial evaluation (including model-based simulation) of the keyboard interface suitable for older adults having dyslexia, and (3) observe the effect of the proposed keyboard on able-bodied older adults’ performance compare to the QWERTY layout. In a broader sense, our work serves as an initial attempt to build a psychological foundation that could support the touchscreen text-entry interface design.