on waking up and growing older

Is the theme clear throughout, or does it become too obscure?

In my opinion, themes/messages in poetry are not easily noticed. They are usually something only the author will notice (at a glance, at least) from what I can tell, this poem is about growing old and how bittersweet it is. I'm not exactly sure what it is you're trying to convey here, but you definitely have something in mind which is always good.

Does the smaller font in the third stanza create a distraction? Is it too hard to read?

The small font only showed up when I went to critique this. Nevertheless, I don't think it creates a distraction. I think it emphasizes what you are trying to say. That grown ups try to chalk things up to imagination, but deep down in our souls we know what we say/think/believe is true (forgive me if I'm wrong, these are just my interpretations)

Is the line about tangled/aging fingers clear?

To be honest, I didn't know that the "tangled" part was supposed to emphasize aging fingers..so no, I wouldn't say that it's particularly clear. I personally think that you could do without the styling of the world tangle as well..seems a bit of style over substance to me. You could have the same effect if you did:

"as frozen fingers tangle
signaling the end of
a child's rationality"

HOWEVER, this is just my opinion. It looks nice the way it is now, but if I wanted to improve this, that is how I would go about it.

Now that I've answered your questions specifically, I'd like to talk about some things that I liked/noticed.

"i met you in our
world torn free of yesterdays,
and far beyond tomorrows.
the sky was a blanketed
white, spreading over our
star-fields and moon-rays."

I'm not exactly sure what you are trying to say in this stanza, but the imagery is very nice. It flows nicely as well. I also particularly liked:

"we cried tears in
negative numbers,
laughing all the while."

I think it really emphasizes the "aging" feel that you are trying to show (at least that is what I'm assuming)

And the ending..just wow, it's very nicely executed. Overall, you have a wonderful poem here that I feel could definitely be improved upon. Even if you chose not to change anything, the poem would still be good! All I recommend is that you try to focus on the content rather than the style/format. I hope that my critique was helpful to you, and if you have any questions, please do not hesitate to <img src="e.deviantart.net/emoticons/n/n…" width="14" height="14" alt="" data-embed-type="emoticon" data-embed-id="266" title="Note"/> me!