What is Meaning of StructField(fieldName, StringType, true)

I am trying to convert a text file to DataFrame. I found using following method instead of case class.
But where is the data type for each field is defined if we go by this method.

            val people = sc.textFile("file:/home/edureka/dmishra/people.txt")
            val schemaString = "name age"
           import org.apache.spark.sql.Row;
           import org.apache.spark.sql.types.{StructType,StructField,StringType};
          val schema = 
                                   schemaString.split(" ").map(fieldName => StructField(fieldName, StringType, true)))
           val rowRDD = people.map(_.split(",")).map(p => Row(p(0), p(1).trim))

           val peopleDataFrame = sqlContext.createDataFrame(rowRDD, schema)
           val results = sqlContext.sql("select name,age from people")

scala> results.dtypes.foreach(println)

Where is the data type assigned for data frame. How to define age as integer data type in this case.