There are many parameters to consider. The caffeine clearance is influenced by genetics, environmental factors, age, drug interactions, pregnancy, illnesses, day and time of day, habituation, what species you look at, etc.
We do not have a complete picture in terms of perfect predictability. But we have quite a few individual lines of cause and effect cleared up to a certain degree.
Caffeine is absorbed in the intestine quite rapidly and almost completely. Then generally 97% are metabolised into 'something' and only 3% excreted as is, on average. Caffeine concentration is characterised in half life.
Drinking grapefruit for example before drinking coffee increases that half life, as the fruit contains quite significant levels of naringenin, bergamottin and hydroxybergamottin. These substances have in common that they inhibit cytochrome p450 in the liver (effecting quite a few drugs by the way). This effect was only found out in 1989 by chance.
Calculating all the variables will not be possible in this answer. Let's focus on genetics of caffeine pharmacokinetcis in humans.
Jakob Strube: "Studie zu erblichen Einflüssen auf die Pharmakokinetik von Midazolam und Koffein.
(Study for the evaluation of heritability of midazolam and caffeine pharmacokinetics)", Dissertation, Georg-August-Universität Göttingen, 2015. (PDF)
This small study found an unexpectedly marked hereditary component in caffeine clearance and also gave a range from own measurements and compared those with previous literature:
Clearance/F* [ml/min] 40 - 431 own measurement
Clearance/F·KG-1* [ml/min·kg- 1] 0,35 – 5,08 own measurement
1,12±0,3 Newton et al. 1981
2,20±1,02 Lelo et al 1986 a
2,07±0,96 Lelo et al 1986 b
2,2±1,67 Kamimori et al. 2002
1,58±0,54 Perera et al 2011
t1/2 [Minuten] 97,6 - 735 own measurement
meist 246 - 342; bis zu 600 Lindopharm GmbH 2004
162 - 744 Newton et al. 1981
246±78 Lelo et al. 1986 b
240 - 300 Kot und Daniel 2008
330±114 Perera et al. 2011
Cmax [μg/l] 668 - 1984 eigene Messung
1170±980 Kamimori et al. 2002
750±250 (normiert auf 50 mg-Dosis) Perera et al. 2011
Tmax [Minuten] 26 - 200 eigene Messung
30 - 40 Lindopharm GmbH 2004
30 - 90 Newton et al. 1981
60 Perera et al. 2011
85,2±54 Kamimori et al. 2002
V/F [l] 22,9 - 68,7 eigene Messung
V/F·KG [l/kg] 0,38 - 0,81 eigene Messung
0,52 - 1,06 Lindopharm GmbH 2004
0,5 - 0,75 Kot und Daniel 2008
0,781±0,208 Kamimori et al. 2002