riddle - I am the last of the three

With hopeful eyes, you gaze at me

Hoping to catch up

Never do you really see

The drink that's in your cup

You think that I've got all the answers

And for all I know, I might

I might have the cures for colds and cancers

But you have to give me the might

You never know what secrets I hold

The gifts and curses I bear

Wait long enough, and you'll have been told

The knowledge I can share

What am I?

Answer

Are you

The future?

Title: I am the last of the three

Past, present, and the future

With hopeful eyes, you gaze at me
Hoping to catch up
Never do you really see
The drink that's in your cup

Kids can't wait to grow up, and in many western cultures it's common to expect that the future brings better things, even though we would probably be better off concentrating on what we already have ("the drink that's already in our cup"), trying to find happiness there.

You think that I've got all the answers
And for all I know, I might
I might have the cures for colds and cancers

But you have to give me the might

Maybe things actually will get better, but not without us, in the present, putting in the effort.

You never know what secrets I hold
The gifts and curses I bear

The future moves ahead just as quickly as the present, so we can never know the future.

Wait long enough, and you'll have been told

The knowledge I can share

As you grow older, you learn things that were, from your earlier point of view, in the future, so you get to know your portion of that future. And then the future cannot tell you any more knowledge, because you'll die. Possibly in a freaky atomic bear-shark-hybrid related incident. You don't know that you won't!