Better ways to translate 积极?
i think proactive and enthusiastic are pretty good translations. you typically use 積極 to describe such qualities in a younger person who's eager to learn or do something but still humble to listen to advice, so it's not used a lot to comment on older people, though you can also use it to describe someone who's new to a role and wants to do a good job. e.g. a newly elected president (who's never been a president before). maybe that's what you feel is missing from the english words? 

same thing for the opposite adjective 消極, which also lends itself better to describe younger people IMHO.