People used to ask Ken Nordtvedt all the time "How old is I-L233 'Western'" (for example). And Ken made the point that there were two different ages to consider:
1) when did the most recent common ancestor of I-L223 "Western" and its sister clade I-L1287* "Alpine" live?
2) when did the most recent common ancestor of all living I-L233 'Western' men live?
I think usually people were interested in question 1) but Ken was more interested in 2). He made the point that for all of human history almost every male line died out/daughtered out, and human populations stayed nearly the same, but at some point in the last few thousand years, populations started to increase continuously up to the present. For some Y-DNA haplogroups (I-M26 "Sardinian") this expansion started 8,000+ years ago, but for others it was much more recent (maybe the last 2,500 years for I-L233 for example).
Ken had some useful trees on his website that showed this difference with what he called arrowheads indicating the start of the expansion ---->
Ken's tree from 2011
I tried to make his trees easier to interpret with tree drawings like these:
my blog in 2011 from wayback machine
Recently several papers have been published making Ken's point about very few surviving male lineages until recent expansions, see Dienekes' summary of here: http://dienekes.blogspot.com/2015/05/more-y-chromosome-super-fathers.html (This paper talks about recent superfathers and starlike expansion in Europe for I1, R1a and R1b, and long branches with deep-rooting nodes" for E1b-M35, G2a-L31, I2-P215, J2-M172, L-M11 and T-M70. Of course there are recent superfathers and starlike expansion in some branches of I2, for example for I-L233 "Western" and I-CTS10228 "Dinaric".
And I like this paper's Fig 1 which uses triangles to show the recent expansions:
http://dienekes.blogspot.com/2015/03/bottleneck-in-human-y-chromosomes-in.html
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