The Collaborative International Dictionary
intestable
intestable \in*tes"ta*ble\, a. [L. intestabilis: cf. F.
intestable. See In- not, and Testable.] (Law)
Not capable of making a will; not legally qualified or
competent to make a testament.
--Blackstone.
Wiktionary
intestable
a. (context legal English) Not legally permitted to make a will, as by reason of being under the age of majority or mentally incompetent.