The nested aggregator delegates to all nested docs that parent doc matches with.
The easiest to get what you want is to repeat the range filter in the aggregations like this:
{
"aggs": {
"in_to_views": {
"nested": {
"path": "views"
},
"aggs": {
"my-filter": {
"filter": {
"range": {
"views.dob": {
"gte": "1980-09-15",
"lt": "1990-09-15"
}
}
},
"aggs": {
"country_count": {
"terms": {
"field": "views.country"
},
"aggs": {
"back_to_ads": {
"reverse_nested": {}
}
}
}
}
}
}
}
}
}