I guess ...
Dropdownlist could have only one text datafield.
Your sql command have 3 columns in one row not one column
name | surname | age
sorgu = New SqlCommand("SELECT name, surname, age FROM veriler WHERE name=@name", database)
DropDownList2.DataSource = kisiler
DropDownList2.DataTextField = "name"
DropDownList2.DataTextField = "surname"
DropDownList2.DataTextField = "age"
DropDownList2.DataBind()
first line you put the value in field name in datatextfield
second line you put the value in field surname in datatextfield
and the last you put the value in field age in datatextfield
so your field age show in dropdownlist
^^