The Eidolon is not allowed to select Ability Increase at lower levels. According to the rules, they should be able to select 1 ability score with each evolution and again after 6 levels. Rule pasted below, evolution can be applied once per ability and then again every six levels. There is no mention of a minimum level.
An eidolon grows larger muscles, gains faster reflexes, achieves greater intelligence, or acquires another increase to one of its abilities. Increase one of the eidolon’s ability scores by +2. This evolution can be selected more than once. It can only be applied once to an individual ability score, plus 1 additional time for every 6 levels the summoner possesses.