I do not know if there exist rules for elder Kuei-Jin chargen. So I'll try to summarize the Kin-jin (Kindred) rules.
This one is from Dark Ages: Vampire which, methinks, has the latest incarnation of downtime maturation rules.
The basic idea is that in downtime characters are much less active than when blood flows freely.
Characters get Maturation points based on the time spent in any given downtime period, as below.
- 1-5 years -> 1 per year (1-5 pts)
- 6-35 years -> 1 per 5 years (6-10 pts)
- 36-135 years -> 1 per 10 years (11-20 pts)
- 136-500 years -> 1 per 20 years (21-40 pts)
- 501-750 years -> 1 per 25 years (41-50 pts)
- 751+ years -> 1 per 30 years (51+ pts)
Maturation Points (MPs) may be spent at basically the same rates as XPs. But for elder vampires (above 200 years), XP costs increase (but MP costs don't).
It is very complicated, and is even more so as Maturation Point gains and costs depend on the character's activity level in any given century/decade. You should check out the Dark Ages: Storyteller's Companion, pp. 69-75.
If you want less complexity, you can design elders from scratch as you would a neonate, just with more points. The rules are also in the same book, on pp. 75-77. Summary is as follows:
- Attributes: 10 / 7 / 5 (above the free rating of 1 in each)
- Abilities: 20 / 12 / 8
- Advantages: 10 Discipline dots (min. half in clan), 15 Background dost, 7 Virtue dots (above the free rating of 1 in each), base generation is 9th
- Road rating (Humanity, what-have-you) is decreased by 1 for every 150 years of activity
- Freebies: 30 pts for a basic elder of 201-350 years, plus 15 pts for every 150 years of beingg active (meaning loss of Road)
Now, as to the Kuei-Jin, you may proceed with the XP-MP method, which is quite straightforward, as XP is XP in both on the East and the West side.
If you go with the chargen-build method, Attributes, Abilities, Backgrounds and freebies should be as above for Kindred, and I'd give 7 free dots in Disciplines, 6 for Chi Virtues and 2 for Soul Virtues (and the free basic dots as for young characters). And then spend the truckload of freebies as per the KotE core book. I checked some elder Kuei-Jin NPCs in the Tokyo and Hong Kong books, and their freebie levels (very approximative) seem to take them to the upper echelons of their corresponding dharmic age ranges.