Larian breaks down the creation of Baldur's Gate 3, from memorable characters like Astarion and The Emperor to its various endings.
Therefore, it would be sensible to infer that Astarion was at minimum level 11, although he may have been higher at level 12 or 13. Finally, Shadowheart, who was a member of the Sharran Cloister of Sombre Embrace in Baldur's Gate. Looking at the other Sharran that can be encountered...