How to filter an elasticsearch global aggregation?

In my opinion this is the typical use case of a post_filter. As the doc says:

The post_filter is applied to the search hits at the very end of a search request, after aggregations have already been calculated

Your query will look like:

{    "post_filter":{       "terms":{            "family_name":"Brown" //filter_1        }    },   "aggs":{        "young_age":{            "filter":{                "range":{ "lt":40, "gt":18 } //filter_2            },            "aggs":{                "age":{                    "terms":{                        "field":"age"                    }                }            }        }    }}

In this case the search hits are all the documents in the index. Then the aggregation is calculated (before filter_1). And after that the post_filter with the filter_1 will be executed.

Edit: As you said in your commend you have many aggregations and only one that shouldn't be affected by filter_1 I fixed your query using global aggregation

{  "query": {    "filtered": {      "filter": {        "term": {          "family_name": "Brown"        }      }    }  },  "aggs": {    "young_age": {      "global": {},      "aggs": {        "filter2": {          "filter": {            "range": {              "lt": 40,              "gt": 18            }          },          "aggs": {            "age": {              "terms": {                "field": "age"              }            }          }        }      }    }  }}

globals and filters are not allowed at same level. you have to put filter at one level inside to global aggregation.

something like this should do for you.

{    "query":{        "filtered":{            "filter":{                "terms":{                    "family_name":"Brown"                }            }        }    },    "aggs":{        "young_age":{            "global":{},            "aggs":{                "filter": {"term": {"family_name": "Brown"}}, #or {"bool": {"filter": {"term": {"family_name": "Brown"}}}}                "aggs": {                    "age":{                        "terms":{                            "field":"age"                        }                    }                }            }        }    }}