How far is the common ancestor for 12 marker match

[hussainr565]

If i have an exact 12 marker match with someone, how far the common ancestor would be?

https://www.familytreedna.com/faq-markers.aspx

According to the above site, it means that there is a 95% probability that the ancestor is no longer than 29 generations and by 29 generation i guess they mean 1000 to 1500 years. Is this assessment correct or not

[bartarl260]

Don't trust the TiP on a Y-12 match. It can be extremely off base.

STR Convergence is a HUGE problem at the Y12 level, and is acknowledged by ISOGG's wiki as having struck as deeply as [email protected]

But as an example in my own case, for [email protected] I am exact match with a clan of Kuwaiti's. Except my patrilineal orgins are from Bohemia(aka Czechia; The Czech Republic, the former Czechoslovakia)

As my username suggests, I'm a "downstream" descendant from R-L260(which another site places as being roughly 4.500 years old).
Except the gentlemen from Kuwait are downstream from R-Z94(which that other site places as being roughly 4,500 years old as well).

R-L260 and R-Z94 are both part of R-1A though, and they're not too distantly related to one another, that other site says you only need to go back another 500 to 1,000 years for them to find a common ancestor. somewhere between 5,000 and 5,500 years before present(R-Z645).

Now compare this to the Y12 TiP report which gives us a 91.41% chance of a sharing a common ancestor in the past 24 generations. Evidently we have some exceptionally long lived ancestors in our shared tree if that TiP is right and the age estimates based on SNPs are also right, as that would mean "a generation" spans some 210 years.

Meanwhile, none of my closest BigY matches ever show up on my STR match list, at any level. But as my closest BigY match(that isn't close family) is at GD16 by Y111, that's not surprising.