Ghouls can probably store more effective Blood Points by drinking elder's blood, but that isn't the only way.
I'm aware of five references relevant to the question. From the Revised Edition core rulebook, page 140:
When drinking from elder vampires, each blood point taken may be so concentrated that it is actually worth two-- or more!-- normal blood points in use. Thus it is possible obtain a vast amount of blood points by partaking of elder blood, though such prized vitae is rarely available to neonates or even ancillae. Essentially, elders have greater blood pools not because they are bodily larger than younger vampires, but because the blood they ingest is more concentrated in their ancient veins.
Emphases mine. Elder blood isn't more, it's better. It's potentially worth more for vampires that drink it, so, by extension, it would be worth more for a ghoul as well. The total blood volume for an adult ghoul, if poured into a graduated cylinder for measure, would still be ten points' worth, just as for a mortal or high-generation vampire, regardless.
If they get enough vitae regularly, a ghoul can casually hold more blood as well. From Ghouls: Fatal Addiction, page 30:
If fed nightly for longer than a month, a ghoul will begin to assimilate vitae into her bloodstream. After the first month of such feeding, assume that one Blood Point of human blood transforms into vitae per additional night of continuous feeding. This vitae osmotically permeates the body without the need for draining the ghoul's human blood. This conversion continues at the rate of one Blood Point per night, until the ghoul holds a full 10 points of vitae.
The phrasing is inconsistent here, where human Blood Points are definitely a measure of volume and not potency, while for vampires it's both simultaneously. The easiest way to bridge it here is probably to treat the vitae as with vampires and leave human blood as volume alone, but I wouldn't say that that is clearly indicated by the text.
There is also an optional rule that can increase a ghoul's supply of vitae. A ghoul can replace its own blood with vitae, increasing the total amount stored beyond what can be drunk in one sitting. From Ghouls: Fatal Addiction, page 28:
A ghoul has a potential Blood Pool of 10, just like a human or a 13th-generation vampire but this is normally presumed to be filled with human blood. [...] A human ghoul may comfortably drink two Blood Points of vitae (this is the amount that fits in the digestive tract). [...] [b]ut only two Blood Points may be absorbed in this fashion. Further drinking does no good unless the ghoul wishes to risk an overdose.
If a ghoul wants to store more blood immediately, she must give up some blood from her circulatory system. Usually the domitor drains the ghoul appropriately (an automatic feat); independents may need to make a trip to the Red Cross or do it themselves at home (Intelligence + Medicine, difficulty 6). A successful roll allows the ghoul to drain her blood and replace it with the domitor's blood in such a manner that she loses no Health Levels in the process; failure indicates that the ghoul loses one to three (Storyteller's call) Health Levels from blood loss before the transferal is effected.
This would allow for 10 points of vitae in a ghoul, and 0 points of human blood.
Regarding an "overdose" (which may yield a couple of Blood Points' worth of vitae), from Ghouls: Fatal Addiction, page 31:
Ghouls can take in more vitae than their stomachs or veins can comfortably handle-- but this often causes dangerous side effects. For each point of Stamina a ghoul has, she can "cram" an extra Blood Point into her gullet or veins. If a ghoul imbibes more vitae than she can contain, she must make a Stamina check (difficulty 8). If she succeeds, she may use the excess blood normally.
If we combine the previous three references, a ghoul may even be able to store more than ten Blood Points' worth of blood volume, in addition to any extra potency the vitae itself might have. Assuming "normal" vampire blood concentration (not elder blood), the ghoul gains 10 points of vitae by completely replacing the ghoul's human blood, then comfortably drinks two more Blood Points' worth for a total of 12 (circulatory system plus stomach/intestines). Should the ghoul wish to risk the Stamina check, the stored volume might be even higher.
As mentioned in the question, older ghouls can gain a larger blood pool without any stated or implied need for elder blood. From Ghouls: Fatal Addiction, page 29:
On the other hand, elder ghouls gain some benefits-- in many ways, such prolonged exposure to vitae metamorphoses them into something not quite human. Elder ghouls and revenants gain additional "storage capacity": for each century of life, an elder revenant gains one extra point in his Blood Pool, while an elder ghoul can comfortably drink one extra Blood Point (i.e., a 150-year-old ghoul can hold three blood points in the stomach, a 210-year-old ghoul can hold four, etc.). Elder ghouls who are not revenants may also gain additional Blood Points beyond their 10, but at the rate of one per two centuries of life (so an 850-year-old ghoul has a Blood Pool of 14, 10 which can be drunk without bloodletting).
This may not matter for a newly made ghoul, but a 1d10 might not even be the right die for an elder ghoul!
