Good two year olds do defeat good older horses and for more than 60 years, circa 1864 until 1924 or so, The Jockey Clubs of every state in America carded All Ages races in which two year olds ran against top older horses. The history of racing in America is peppered with good two year olds defeating good older horses. The problem arose after the races when the two year olds came back sore and mentally stressed out as it was too much stress on their younger and smaller bodies so horsemen dropped the practice somewhere in the mid 1920`s.
There are a few famous cases of two year olds beating four year olds.
Plaudit owned by John Madden, foremost breeder in the 1890`s, won the Champagne Stakes in 1897 decided to square off against Ben Brush 1896 Ky. Derby winner. Ben Brush was the top 4 year old at the time owned by Mike Dwyer who also owned Gravesend Race Track in Brooklyn NY.
So on Sept 29, 1897 at Gravesend Park, a race between the two took place and in a 5 horse field Plaudit won and beat Ben Brush by a head. These men believed a race between the two horses is the only way to settle the matter of who was best. They did not think abstract comparisons between horses that never ran together proved anything.
Other noteworthy two year old winners (against older horses) include:
Pan Zareta who did it in Mexico 1912 (this filly once beat Old Rosebud Ky. Derby winner)
Comely in the Fall High Weight at Aqueduct 1914
Sarazen 1924 Champagne Winner went 10 -0 as a two year old and won two races against Maryland’s best 4 year olds at a mile each time.
There are many more cases of two’s beating 4`s but the list would be too long to post here.
