What happens to Venus blessing if a (female) character gets older?
Someone who looks like 35 may still be seen as attractive, but what happens if she is 50 years past gauntlet and looks like she's 70? Is she good at seducing old men (and interested women) only, or do people of all ages still want her?
Does she look younger?
Venus' Blessing gives you a bonus when interacting with "sexually compatible characters in appropriate situations".
Who is considered "sexually compatible" may well change as the character grows older. This of course applies to both male and female characters.
Definitely not.
"sexually compatible" with 20 years old doesn't make sense to me.
Even the ugliest hag is beauty in the eyes of the right beholder.
"sexually compatible" with red hair.
"sexually compatible" with christians.
"sexually compatible" with married people.
None of those should make sense. And even if it did, Venus' hair wouldn't turn red.
Interesting question. Certainly a 70 year old woman with Venus Blessing would have a broader appeal than an equivalent woman without it. Maybe not "younger" but with a more vibrant and lifely energy.
Or alternately eliciting loving sympathy from people who want to gently make love to her. And some people just have a thing for older women, and this is (one of) the woman they have a thing for...
For a lovely example, just view again Katherine Hepburn as Eleanor of Aquitaine in Anthony Harvey's THE LION IN WINTER.
Here's a remarkable take on her acting then:
Hepburn quickly returned to acting after Tracy's death, choosing to occupy herself as a remedy against grief.[182] She received numerous scripts[183] and chose to play Eleanor of Aquitaine in The Lion in Winter (1968), a part she called "fascinating".[184] She read extensively in preparation for the role, in which she starred opposite Peter O'Toole.[185] Filming took place in Montmajour Abbey in the south of France, an experience she loved despite being—according to director Anthony Harvey—"enormously vulnerable" throughout.[186] John Russell Taylor of The Times suggested that Eleanor was "the performance of her ... career", and proved that she was "a growing, developing, still surprising actress".[187] The movie was nominated in all the major categories at the Academy Awards, and for the second year running Hepburn won the Oscar for Best Actress (shared with Barbra Streisand for Funny Girl ).[188]
AFAICT, the underlying question is "can older characters have sex appeal".
We know 2 things: People don't stop having sex at 25, and people in retirement homes still find ways to get naughty with each other.
=> The answer should very clearly be yes.
The difference is, a character with Venus Blessing, whatever their age, is perceived as more attractive than normal.
So, how does age enter the fray?
Well, through additional difficulty.
If someone aged 70 is trying to seduce a 20 years old, they'll have to make a roll. This roll will probably have an increased difficulty, which Venus blessing will make easier to beat.
So, Hot Granny? All things being equal, yes 
Part of it is also simply a matter of the characters. If your 70 year old with venus blessing is trying to seduce a 20 year old who is grossed out by old people then you are not considered sexually compatible. If the seventy year old woman is trying to seduce a 20 year old man who is constantly worried about getting a girl pregnant and has no problems with age she is definitely sexually compatible. It isn't just about gender preference.
I guess the positive aspect is that she's right int he age bracket for seducing archmagi - and she can always use cosmetic imaginem...
I'd also note that age difference in this way (older women) wasn't considered weird until, like, the 19th century.
Money matters. Age, not so much.
That is true, up to a point. Keep in mind that older women in the middle ages generally weren't as old as older women today (nor were older men for that matter), and the ability to bear children was also a factor (though with money that could be overcome). Both money and fertility however were more factors in marriage than in a dalliance. There were however a lot of other factors such as relative power levels, which quickly get into territories that many people will want to keep out of their games, so its probably best to stick with a YSMV label here, and maybe throw in the comment that decrepitude may be more of an issue to attractiveness (and of course presence decreasing with age) than the actual number of the age itself.
I mean 50 is pretty old for the 13th century but when Cher was 50 she was still pretty hot...(This actually came up as a weird side topic on a daytime TV show at the time and this was the consensus opinion, so the reference is not quite as random as it seems)
Heck, she's 75 now and still pretty attractive...
Side note: a maga 50 years past gauntlet probably doesn't look 70. She might look 40.
Which is not relevant to non-magi, but you did specify.