IshGen 149:12 :ܬܘܠܬܐ܂ ܗܢܘ܂ ܒܪ ܬܠܬ ܫܢ̈ܝܢ‏ : t', i.e., three years old
See the entire entry for tullāṯ, tullāṯā v.n.D third repetition