The earliest confirmed derived rs4988235 is I6561 ~4000 BC R1a1 sample from NE Ukraine.
The earliest potentially derived sample is ~7200 BC WC1 who was possibly heterozygous at rs4988235.
"WC1 is heterozygous at rs4988235 (C/T(-13910)) ... Analysis of the
specific read groups from which these reads derived along with their base quality and mapping
scores did not show signs of contamination. However, the small number of derived reads present at each LCT site, particularly the ratio of derived/ancestral reads (1:10) in WC1, leads
us to suspect they may be erroneous."
https://science.sciencemag.org/conte...oushaki.SM.pdf
"WC1 Early Neolithic 7455–7082 2/11"
https://genetiker.wordpress.com/2016...-ancient-iran/