160 Eager beaver

(PW) ambitious, hard working

Charlie gets to work at 7:00 am everyday.  He is an eager beaver.

(free) n. Informal

One that is exceptionally, often excessively industrious or zealous: "The eager beavers of industry seldom reach their potential, much less rise to the top" (Newsweek).

Informal a person who displays conspicuous diligence, esp one who volunteers for extra work

(MW) Function: noun  Date: 1943

a person who is extremely zealous about performing duties and volunteering for more

(your) 

An exceptionally zealous person, one who habitually takes on more tasks or works harder than others. For example, Bill is a real eager beaver, always volunteering to stay late. This expression became especially popular during World War II, applied to recruits anxious to impress their commanding officers by such behavior. [First half of 1900s]

Slang a person characterized by much, or too much, industry, initiative, or enthusiasm

(Lexicology)

(n) an alert and energetic person