Pausanias explains when the different events were introduced at Olympia.
After king Oxylos, who organized the games too, the Olympic games were no longer held until Iphitos. When Iphitos restored the games, like I have said before, people had still forgotten the old times. Little by little the memory came back and every time they remembered something, they added this to the games.
Here is the proof: since the olympiads are recorded continuously (776 BC), first the prize was for the stadion run, and Koroibos of Elis won. … In the 14th olympiad (724 BC) the diaulos was added. Hypenos, a man from Pisa, received the olive crown for the diaulos and in the next olympiad (720 BC) the Spartan Akanthos won the dolichos. In the 18th olympiad (708 BC) they remembered the pentathlon and the wrestling. Again two Spartans won: Lampis in the pentathlon and Eurybatos in the wrestling. In the 23th olympiad (688 BC) they offered a prize for the boxing. The victor was Onomastos of Smyrna, which by this time was already part of Ionia. In the 25th olympiad (680 BC) the race with full-grown horses was added to the program. Pangondas of Thebes with his four-horse chariot was proclaimed as victor. In the eighth olympiad hereafter (648 BC) the pankration for men and the race on horseback were introduced. Krauxidas of Krannon won with his horse and Lygdamis of Syracuse beat all other participants in the pankration.
There is no record of the events for boys in the old times. The Eleans established these as they wished. The prizes for the stadion and the wrestling for boys were for the first time offered in the 37th olympiad (632 BC). Hipposthenes of Sparta won the wrestling, Polyneikes of Elis the stadion. In the 40th olympiad (620 BC) boys were for the first time called up for the boxing and Philytas of Sybaris beat his opponents.
The race in armour was accepted in the 65th olympiad (520 v.C.), as a training for war, it seems to me. The first victor of the runners with shield is Damaretos of Heraia .
The race for two-horse chariots of full-grown horses was introduced in the 93th olympiad (408 BC). Euagoras from Elis won. In the 99th olympiad (384 BC) they decided to introduce also a race for four-horse chariots for foals. Sybariades of Sparta won the crown with his chariot drawn by four foals. Later they added a race of two-horse chariots for foals and the race on horseback for foals. They say that lady Belistiche from the coast of Macedonia was proclaimed as victor of the race with two-horse chariots and Tlepolemos of Lycia of the race on horseback. He in the 131th olympiad (256 BC), Belistiche with the two-horse chariot three earlier (268 BC). In the 145th olympiad (200 BC) the pankration contest for boys was instituted and Phaidimos, an Aiolian form the city of Troas, won.
From other sources we know that Belistische won the race for two-horse chariots for foals not in 268, but in 264 BC. In 268 BC she also participated in the games, but then she won the race for four-horse chariots for foals.
Pausanias' books about Elis