how to subquery with aggregate

[PeterShinners]

I have a mysql table of key and value pairs for a list of entities, the schema looks like

entity: int
key: varchar(36)
value: varchar(36)

When looking up my entities with SQL I use a subquery with an aggregate to include this information.

select
   name,
   (select json_arrayagg(json_array(key, value)) from labels where labels.entity=entity.id) as labels
from entity
  where entity.age > 20

I'm experimenting with converting my direct SQL code into Ibis queries. I haven't been able to figure out how to match this subquery. I have gotten something fairly close, but it ends up as a performance bomb because it aggregates all the data in the table before filtering by id.