Surya Siddhanta
परमायुः शतम् तस्य तयाहोरात्रसम्ख्यया।आयुषो<र्धमितं तस्य शेषकल्पोड्यमादिम: ॥
And the age of Brahmá consists of a hundred years—according to the enumeration of day and night (mentioned in the preceding śloka). One half of his age has elapsed, and this present Kalpa is the first in the remaining half of his age.
english translation
paramAyuH zatam tasya tayAhorAtrasamkhyayA।AyuSo<rdhamitaM tasya zeSakalpoDyamAdima: ॥
hk transliteration by Sanscript