The influence of second language (L2) on first language (L1), known as L2 transfer, has been proposed as a fundamental driving force of L1 attrition. This inquiry tested the differential attrition of verb aspect and tense in L1 (Russian) under the influence of L2 (German) grammatical properties. It also explored whether the age of bilingualism onset and the amount of exposure to L1 modulate this L2 transfer effect.