aggregate max against date field returns unformatted date

[kti_sk]

queries such as
{ 
  "aggs": {
    "max_startTime": {
      "max": {
        "field": "startDate"
      }
    },
    "min_startTime": {
      "min": {
        "field": "startDate"
      }
    }
  }
}

return s140834239392... instead of nicely formatted date.
The field is maked as date type.
Am I using the query wrong? is there a way to 'cast' the data to date?

thanks

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