The core of this suggestion: Have some kind of "Last grew" timestamp on pet pages.
Specific stuff:
- Probably only for "Still growing" pets (including pets that go through multiple stages on the adult lineart). Not much benefit for fully-grown pets.
- Could take on a whole bunch of forms...
- Age 7 days (last grew at 7 days)
Growth Still growing - Age 7 days (last grew today)
Growth Still growing - Age 7 days (last grew 2 minutes ago)
Growth Still growing - Age 7 days
Last grew 7 days/today/2 minutes ago
Growth Still growing
(probably would be better to use one of the other forms if the Last grew is only going to be there for still-growing pets) - Age 7 days
Growth Still growing (last grew at 7 days/last grew today/last grew 2 minutes ago)
(this is probably the best if the addition will only be there for still-growing pets, because the disappearance of the note will make the most sense with this form)
- Age 7 days (last grew at 7 days)
Benefits people who are trading still-growing pets in any month, but ESPECIALLY during rerelease season! Can also cut down on scammers (even though they're punishable, prevention > treatment) which is great since those scammers usually won't be caught right away, although I don't know how often staff have to deal with cases of users falsely claiming a pet grew on a certain date
It's been over 10 years since 
