Compose, on scratch paper, a short paragraph in which you describe the birthday celebrant, focusing on how much the person means to you and other loved ones. Avoid words like "beauty," "happy," "truly" and "very," which don't mean much anymore. Instead describe something physical, perhaps the natural world, which is an old custom in odes, and put the person in it. Make an effort to include each letter of the name as the first letter of a word. The words can land almost anywhere in the paragraph as long as there are at least a few words between them. For example, If the celebrant's name is Thomas, begin with a word that starts with T and continue writing:
"The roses shift in the breeze when you walk by, as if they long for you. Hollyhocks pay attention when you look at them. Outside the yard, hills rise up, and trees mass in crowds. The world wants to receive you, as if you were born on this very day, 25 years ago, so that we could all celebrate you."
Aim for meaningful lines more than for rhyme. You do not need to rhyme the last word of every line. In fact, you do not need to use rhyme at all. If you end lines with rhymes, the poem may sound too singsong, like a children's nursery rhyme. You will also make the job that much harder.
Break the paragraph into the appropriate lines in the next draft. In the example above, start line one with "The roses..." Start the second line with "Hollyhocks..." Move on to "Outside...," then "mass in crowds. The world..." and then "as if you..." and finally to "so that we could all celebrate you."
Note that a line does not have to be a complete sentence, but it may be. However, if you are letting a sentence spill over into the next line -- a poetic technique called enjambment -- the first word on the next line should start with the corresponding letter of the person's name, as in "mass" for Thomas. Also, don't be afraid to start a new sentence in the middle of a line.
Revise to tweak your poem, clean up spelling and punctuation and take care of other small matters. Then type it or write it out in a blank card to present to your loved one.