Lively around mid-May, like the Highlands? (4,2,5)
I believe the answer is:
full of beans
'lively' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for full of beans that I've seen before include "Might maracas be" , "energetic" , "after feast in seedy restaurant?" , "Very lively and cheerful" , "like a cowboy after a meal on the range?" .)