The first reaction should be Brahms... Unlike other composers, he had his own symphony works very early. Brahms took 21 years to compose his First Symphony, and it was not until he was 40 years old that his First Symphony was completed. The key point is that this guy took so long to write not because he was delayed by other things, but because he was really thinking about it. He disdained writing simple works, determined to use Beethoven as a benchmark, and hoped to write works of the same height as Beethoven. So, by the time he finished writing the First Symphony, he was already 43... But it lived up to expectations, and his First Symphony was also called the Tenth Symphony after Beethoven. This person has always called himself a classical musician and wanted to imitate Beethoven, but he couldn't. Judging from the musical form, proper romanticism has not escaped. Others... Mahler and Bruckner can also be regarded as late bloomers, but I don't know them very well... So, that's all for now...