Mixing old and new reviews is confusing, and as a guest I would want to see latest and up-to-date reviews, because that's the situation going on right now.
Old reviews may reflect something good or bad that might not even be relevant anymore!!!!!
Response from Airbnb
We agree that older reviews may not reflect current reality as you continue improving your listing and your hosting skills, often based on guest feedback. However, our research has shown that displaying reviews from guests of the same language and country leads to more bookings, and we want you to get as many bookings as possible.
The reviews that a guest sees on your listing are prioritized first by the guest’s native language and country, and second by chronological order. In some cases, older reviews may appear above more recent ones that aren’t in the guest’s native language or from the guest’s home country.