Final answer:
Johann Sebastian Bach has been decomposing the longest among the given composers.
Step-by-step explanation:
The composer who has been decomposing the longest out of the four options provided is Johann Sebastian Bach. Bach was born in 1685 and died in 1750, making him the oldest composer in terms of lifespan. He was a prominent figure in the Baroque period and is known for his contributions to choral music, organ works, and instrumental compositions.