Rashi on Numbers 15:6/רש"י על במדבר ט״ו:ו׳

1או לאיל OR FOR A RAM [THOU SHALT PREPARE etc.] — This means: and if it be a ram [thou shalt prepare, etc.]”. Our Rabbis, however, have interpreted the word "או," “or”, as being intended to bring also the פלגס (a lamb beyond the age of a כבש and below that of an איל) under the law of the drink-offerings prescribed for a ram (i.e. that the animal in its intermediate age is regarded as full grown as regards the נסכים) (Chullin 23a; Menachot 91b).