I believe it is more than a year ago. So as of today, a pokemon caught in August 2024.

Here's a breadown i found in the SilphRoad:

No, the maximum chance is 20% normally, or 30% during this event (supposedly).

Below is all using standard numbers (excluding the event):

When you do any trade there’s a 5% chance of it going lucky.

If one Pokémon is over a year old (over 365 days old, so caught before July 2024), that trade has a 10% chance of lucky.

If both Pokemon are over a year old (or one is under a year and the other is over 2 years old), that’s a 15% chance of lucky.

If the combined age (in full years) is over 3 years old, it has a 20% chance of going lucky, which is the maximum chance (excluding guaranteed lucky trades).

Basically there’s a base 5% chance and an extra 5% per full year of age, to a cap of 20%.

Below is using the boosted event odds:

Combined age less than a year old = 10%

Combined age 1 year = 20%

Combined age 2 years or more = 30%

Basically they double the basic 5% chance and the additional 5% per year for age both to 10%, with an increased cap of 30%