There is a wide range of age estimates for Y-chromosome haplogroups connected to estimates for expansion of modern Proto-Eurasians. See for example
- Robb 2012: CDEF-M168 54,000-66,000 years, J 21,000-28,000 years,
- Wei et al. 2013: CDEF-M168 57,000-74,000 years,
- Francalacci et al. 2013: F-R haplogroup ca. 110,000 years
- Iñaki Comas et al. 2013: MTBC age ca. 70,000 years
- S. Gopalakrishnan et al. (unpublished): Eurasian expansion ca. 75,000 years
Our current estimate is based on Y-sequences (SNP counts) and a intermediate calibration point set at CDEF-M168 (see phylotree.org/Y) with 70 ka (kiloannus = thousend years) ago according to Karafet et al. 2009. The matching Y-Mutation rate is ca. 0.8×10^-9 mutations/nucleotide/year.
Using these guidelines J2 lived approx. 30,000 years ago probably in or near Northern Fertile Crescent. Full Y-Sequencing at high coverage (FGC, BigY) of enough J2a and J2b as well as J1, I, KLT, H, G, F, C and DE samples will make more accurate estimates possible maybe in mid or late 2014.
If you like to follow/join discussion on J2 haplogroup ages, look at this MolGen Forum thread: age of main J-M304 nodes (J1, J2, J2a, J2b) haplogroup.