It says here that Avraham was 75 when Hashem told him to go. Shmos 12:40 implies (see Rashi there) that he was 70 at the Bris Bein ha'Besarim (in Eretz Yisrael at the end of Parshas Lech-Lecha)!
Da'as Zekenim, Chizkuni, Tosfos Berachos7b): Avraham Avinu went to Eretz Kena'an twice. Until Shishi (Bereishis 15:6) discusses the second time (when he went there to stay), and from Shishi (Bris Bein ha'Besarim), discusses the first time 1 , after which he returned to Charan. 2 The Torah is not always in order. 3
Moshav Zekenim: Likewise, we find that he was 74 when he defeated the four kings later in this Parshah. (How can he say so? Before the war, Lot went to Sedom due to his wealth after returning with Avraham from Mitzrayim! Tosfos (Shabbos 10b) says that Avraham was 75 when he defeated the kings.)
See Ramban in Shemos 12:41 who explains the four hundred and thirty years mentioned there differently.
Riva (verse 10) supports this from Brachos 7b. It says that Avraham was the first to call Hashem "Adon", and cites Bereishis 15:8. It should have cited Bereishis 15:2! Rather, the Parshiyos are out of order; Bris Bein ha'Besarim was before Pasuk 2. Also, it cannot be that the entire Parshah was said at once. Verse five was said at night, for He asked Avraham to count the stars, and in verse 12 it says that the sun set!