[Siphwho]

Einstein already made his most significant contributions by age 26 and spent the rest of his life arguing against quantum theory, the dominant school of the 20th century. Most modern physicists regard the latter portion of his life a waste in way of contributions.

[abecedarius]

That’s a little misleading — the latter period started around age 40. E.g. Bose-Einstein statistics was from 1918, which would be age 39 if 1905 was 26. The EPR paper was many years later still. Also, you can’t leave general relativity out of his most significant work.