There is no evidence to say how much time has passed between Black/White 2 and Scarlet/Violet but we are introduced to 2 descendants of Unovan gym leaders at Blueberry Academy - Clay's daughter Lacy and Drayden's grandson Drayton. If I had to guess I would say a decade as B/W 2 were released in 2012 and S/V were released in 2022. If there is a time gap like this between them it would be interesting to think about Unova's younger gym leaders move into adulthood (though i have previously debated if Chili, Cress and Cilan are/were teenagers but Iris is/was probably a preteen and Cheren and Roxie are/were) and Burgh ("young man") could now be be a similar age to Brassius,
- during interactions as special coaches Grusha (young adult) called Brassius "old man" but Kofu (middle- aged) addressed him as "my boy". This might suggest Brassius is in his 30s.