If Gladys will be 40 years old ten years from now, she is 40-10= <<40-10=30>>30 years old currently.
Juanico is 4 years less than half the age of Gladys, meaning he is 4 years younger than 1/2*30 = 15 years.
Juanico's age is 15-4 =<<15-4=11>>11 years.
Juanico's age 30 years from now will be 30+11 = <<30+11=41>>41 years.
#### 41