즐겁다 enjoyable. Note that using 서 before 즐겁다 gives the meaning “glad that or enjoyed ...ing” in English. The idea is cause, followed by result. One may think of the basic meaning of 서 as being sequence (one thing happens and then another). It is formed by removing 요 from the Polite Form and and adding 서. You don’t need to put anything before 서 to indicate tense, as it takes its tense from the verb at the end of the sentence.
는데 is used when one is about to explain something. In English it may be translated by ‘but’ or ‘and’. To make the form, remove the 다 of the Dictionary Form. After a consonant it becomes 은데.
축하하다 to congratulate
태어나다 be born
동갑 same age
살 Counter indicating years of age. It takes the native Korean numbers before it. Note that 스믈 twenty is one of the numbers that loses a consonant before a counter: 스므 살 twenty years old.
시 hours Counter indicating hours. Takes the native Korean numbers before it.