mongodb - query documents by value of field name
Since your keys are unknown you have to convert them to some key value pair using $objectToArray aggregation and then can easily $match with it
db.collection.aggregate([ { "$match": { "points.date[number]": { "$exists": true }}}, { "$addFields": { "match": { "$objectToArray": "$points.date" } }}, { "$match": { "match.k": { "$lt": "7" }}}, { "$project": { "match": 0 }}])