I’ve noticed that some younger cats tend to have pink pads on their paws, whereas older cats have dark brown / black-colored paw pads. Is this due to age (and attendant physiological changes), or merely the accumulation of dirt?
nope! it’s totally about the color of the toes in question.
Cats are fanatics about washing their paws. If a cat has dirty paws, there’s something wrong with it.
My calico cat (peach, grey and white) has pink and black toes. It is all about the toe colour.
It’s like nose color, some cats have pink noses and pink toeses, and some have black noses and toeses. And some have brick colored skin. Some, the blue or partially blue, have blue noses and toes. For Siamese cats, having the wrong color nose leather and paw pads for the point color is considered a fault.
I have one seal point meezer, who has a black nose and black toes, and two orange tabby boys, who both have very pink noses and toes. Even the five year old boy has pale pink skin, he’s a redhead and getting older isn’t going to increase the amount of pigment in his skin. If he went outside, I’m sure that he’d have a sunburned and peeling nose all the time.
My Tiger has a dark nose and black toe pads, except for one pad on her right rear foot. I joke with her that “that’s a spare part off some other cat”. 
An orange cat can have orange cat lentigo, where the pink paws, nose, gums, and other assorted parts get brown freckles with age. My Edison’s parts were all pinky pink when he was a kitten but now freckled with brown.
Stokie, who is a tuxedo cat, has little white socks on his feet. The paw pads where the white is are pink, the rest are black.
As a side note, all purebred Bengal cats have black pads. All black on all paws, that is. However, there noses are not black. But, then neither is mine.
Our part Bengal has the black paws and pink nose. I did not realize that was a breeders trait. She basically looks like a Bengal but was a stray we fostered and then adopted from 4 weeks.
Good for you, I’m sure she is as wonderful as any purebred. And certainly less expensive. 
What color are her eyes? One of ours has hazel color and the other’s are very green.
Other characteristics are that the tip of their tails are black. Their hind legs are longer than the front, so they sort of look like they are going downhill. They frequently love water, sloshing around in the shower, drinking from faucets and ours dip their paws in the water when my wife takes a bath.
Google Bengal cats and you and compare your gal with the pics you’ll find.
My Luna, who is a dilute calico, has three pink paw pads. She has a dark marking on her lower left front leg, and her “palm” on that foot is dark.
Katya is solid gray, and her paw pads are mauve.
This thread needs pictures of cat paw pads!
Her eyes are goldish. She also as the going downhill wildcat look you describe. All the water habits you describe too. We have a small clip of her playing in the deep sink in fact. She looks like a Bengal and acts like a Bengal though she does have the ticked hair which a well bred Bengal apparently would not and she has odd American Curl-like Ears (Spock Ears). This pic shows her eyes and ears off.
Yup, What Exit?, most definitely Bengalish. She’s a real cutie. Very funny trying to catch water drops. Isn’t it interesting that most cats of one breed share so many characteristics, both physical and behavioral?
Very nice of cats to entertain us so.
My theory is most cats are descender from a desert wild cat species but Bengals have a healthy dose of jungle kitty in the mix.
When I get home I’ll get right on that.
I had a very dignified tortoiseshell who had black nose leather…except one tiny pink dot by her nostril. We referred to it as her booger.
My little Fiji is blue all over with mauve toeses and noses.
As far as our cats go, Ariel is a mackerel tabby with a light brown nose and black toes, while Morgan, the tortie, has mostly black with a few pink splotches on her toes and an all-black nose. (Incidentally, the roof of her mouth is also splotchy pink and black, which makes her yawns pretty hilarious-looking)
FWIW, I’ve found that toe/nose colour correlates pretty closely with the colour of the surrounding fur - the darker the fur, the more likely it is that the toe/nose will be black. For example, my sister’s cat Reef has a pale rosy pink nose to go with his mostly-white face.
My kittehs:
#1–flame point Meezer mix, pink toes and nose
#2–orange tabby, pink nose and toes
#3–brindled, mostly black tortie, black nose and toes
#4–brown tabby, brick red nose and black toes
Skin color in general tends to correspond to the fur color. A white spot on the fur usually means that the skin underneath is white or pale pink. A dark spot on the fur frequently has darker skin underneath that area. There are plenty of exceptions, but I’ve had to have meezers shaved for various reasons, and they tend to have darker skin on their points, as well as darker fur.
So a toe with white fur on it is very likely to have a pink paw pad, whereas a darker fur color usually has a brick or black or blue paw pad. My daughter has a grey tabby and white boy, and some of his toeses are pink, and some are black. And he has an adorable little pink nose.