Well, not really, not until it involves in sexual acts
grooming can happen to adults too. it's when there's a power imbalance and the person w power takes advantage of the other person thru manipulation, isolation, exploitation, and abuse.
if the person in power draws boundaries and respects and encourages the other person's autonomy and growth, it's not grooming.
i don't think there's anything wrong when the older person gets worn down by the younger person in a romantic pursuit in fiction bc for a large part it's wish fulfillment for the younger person, but i do expect the person in power to behave differently irl.
would it still be considered grooming if the older person has no intention of romantically loving the younger one? its just that the younger one is adamantly in love with the older one and the older one keeps on rejecting them before deciding to just ultimately acceptinh the affection of the younger one
PS. this is a general observation from past BLs that follow this troupe