Charles Brandon is around court at this time. He is twenty. It makes sense for them to be leading this royal "brat pack" with Prince Arthur, who is now 18. Other courtiers with whom I'm familiar from the era are too young.
Any suggestions?
I think we can look for people a bit older than Arthur, as well. After all, Griffith Ryce is one of his closest allies, and he's eight years his senior. So on that note...
One of Surrey's sons. His heir, Thomas, is a little too old, but his other two sons (
Edward and
Edmund) both seem to have potential. And of course they fit your earlier allusions to the Tudors and the Howards being so tightly knit; and with Surrey as Arthur's tutor, they're probably well-acquainted.
I was hoping to put one of Buckingham's children in there, but it turns out that they are born either ten-twelve years before, or even ten-twelve years after he was.
Buckingham himself is only eight years Arthur's senior. Having the Premier Duke on your side is such an ace in the hole that it would definitely move Henry VII's hand.
If not him personally, an excellent Stafford candidate is his younger brother,
Henry, who did well in OTL under both Henry VII and Henry VIII.
There's also
Richard_Grey, son of the Earl of Kent, soon to inherit the title from his father and then become Knight of the Garter, so obviously he's on good terms with the Royal Family (perhaps because he's Elizabeth of York's first cousin).
Thomas_Grey, Marquess_of_Dorset. The Premier Marquess, so similar to the effect of having Buckingham onside, if somewhat diluted. If he's too old, then his younger brother,
Leonard.
I'm not sure about any younger candidates. Especially since many of them are bound to be part of Henry's retinue instead.
ETA:
Thomas_Stanley, Heir Apparent to the Earldom of Derby, which he'll inherit only a few months after the discussion. He and his younger brother, James (born 1486), are the perfect ages to be in Arthur's court. They're related to Arthur on both sides (by blood to Elizabeth, by marriage to Henry), and their
father and
grandfather both served Henry VII with distinction.