An incapacitated person who has not been judicially declared incompetent may sue or be sued. The mere fact that the action is commenced before the plaintiff moves, pursuant to CPLR 1202, to be appointed guardian ad litem of the incapacitated person is not grounds for dismissal under CPLR 3211(a)(3). CPLR 1202(a) expressly states that a motion for the appointment of a guardian ad litem may be made "at any stage in the action."
Linghua Li v. Xiao, NY Slip Op 06388 (2d Dep't August 28, 2019)
Here is the decision.