What's it called when you take each letter from a word and make new words for those letters?

Acrostic

Google "acrostic poem grandparents." There are a million of them. Since I don't know what you're grandparents are like at all, the adjectives I would come up with may not fit at all. G - gray hair, maybe they don't have gray hair. R - read to me, maybe they don't read to you. E - easy on the eyes, maybe your grandparents are ugly. I don't know. What will make it worthwhile is if it's actually about YOUR grandparents, written by YOU! Only you know your grandparents. So, unless you want it to be as generic as some stupid greeting card, which of course you can Google as I said and will make them feel about as special as nothing at all, get off your lazyass and write it yourself.

Acrostic poem or acrostic wordplay
Try using this adjective page, it may give you some inspiration:
http://www.enchantedlearning.com/wordlist/adjectives.shtml
http://www.momswhothink.com/reading/adjectives-that-start-with-a-to-z-list.html