Srimad-Bhagavatam: Canto 12 - Chapter 1 - Verse 11
Sanskrit:
त्रिंशद्विंशतिवर्षाणि परमायु: कलौ नृणाम् ॥ ११ ॥
ITRANS:
triṁśad viṁśati varṣāṇiparamāyuḥ kalau nṛṇām
Translation:
The maximum duration of life for human beings in Kali-yuga will become fifty years.