I'm adding a brief summary for each of the rare H subclades, including H18 through H100, and any newly proposed subclades. The summary includes samples fromthe H Subclade Discovery Project and GenBank. Feel free to email me a request for a summary of your group (but only for H18 to H100).  Only about 20% of the people who tested the mtDNA full sequence have joined the project and shared their coding region results, so in some cases you might get a better estimate of the size and locations of your H subclade by looking at your FMS match list in your FTDNA account.  Age estimates are approximate and are either from Behar et al. (2012) or from project & GenBank data. Uncertainty estimates are not include, but uncertainty is usually in the range of several hundred to a few thousand years.
(updated Jan 6, 2017)

Behar et al. have an age estimate of about 14,000 years for haplogroup H, and it most likely originated in southwest Asia and the Middle East among early farmers and herders. Haplogroup H and its subclades expanded rapidly in size and and diversity as Neolithic peoples expanded throughout Europe, western Asia and beyond.  It is not yet possible to associate all H subclades with specific Neolithic cultures, although this may become possible as more samples and more ancient mtDNA results become available.


H23 (C10211T) is estimated to be about 4000 years old based on diversity of present day samples. There is an H23 sample from ancient remains found at Halberstadt-Sonntagsfeld, Germany dated to about 3000 years ago.
H23 has 30 samples including: 5 from Germany, 2 from Sweden, 2 from England, 2 from Ireland, 2 from Netherlands, 2 from Russia and 1 each from Poland, Scotland, and Czech. It seems likely that H23 originated in the Steppe region among early speakers of Indo-European languages and was among the migration of Steppe peoples to Europe. 


H24 (A16293G) is estimated to be about 7000 years and has it's greatest diversity in western Europe, including Spain and the Basque region.  Named subclades include:  H24a (C3333T) with an age estimate of 4300 years and mostly found in the UK, Ireland, Germany and Scandinavia;  H24a1 (G5261A,  C16234T) with an age estimate of 3000 years and samples from Ireland, Germany and Austria; H24a2 (G11440A) with one sample of unknown origin; and H24b (G1719A) with 2 samples from the Basque region.


H26 (T11152C) is estimated to be about 10,000 years old and has 58 samples in the project and GenBank (as of August 2014).  An H26 samples was found in ancient remains dated to about 7000 years ago in the LBK culture Germany (Halberstadt-Sonntagsfeld). and this suggests that H26 may have been originated in the Near East and arrived in Europe with the migration of early Neolithic farmers.

H26* has 2 samples, one of which is from Italy.
H26a (A9545G) has 3 samples from Germany, Croatia and Italy.
H26a1 (T13500C) has  18 members with the largest number are from Germany but there are several from the UK and Ireland, and one each from Norway, Poland, Hungary and Slovakia, and H26a1 is estimated to be about 4000 years old. H26a1 seems to be Germanic in its earliest origins.
H26a1a (A14203G) has 3 samples from the UK, Ireland and Norway.
H26a1a1 (T196C  G12651A) ...
H26a1*Group B (5899+C) has two samples from Germany and Scotland.
H26b (T11399C  A12810G  C16320T) ...
H26c (T146C!  A10562G) ...


H29 (A93G  573.XC  A5582G) estimated to be about 10,000 years old.
H29* Group A (13635a) has 2 samples from Italy.
H29* Group B (9156) has 3 samples: 2 Syrian Druze and Iran.
H29* Group C (3398, 4496, 8793, 15110) has 2 samples: England and Germany.


H31 (A7930t  A10771G), estimated to be about 4000 years old.
H31 with no extra mutations has 7 samples: 2 Finland, Italy, Poland, Sweden, UK.
H31* has 6 samples: 2 Scotland, Ireland, Germany, Finland.
H31a (T72g) about 1000 years old, 15 samples: 4 Scotland, 2 England, Germany.
H31b (C15247T) about 1000 years old, 15 samples: 2 England, Norway.
H31* Group C (C198T, C2789T) 3 samples: 2 Sweden, Norway.


H47 (T9530C  C12633T), estimated to be about 9000 years old.
H47* has 5 samples from Italy, Romania, Ukraine and Armenia.
H47a (T152C!  T8756C  T13020a), 2500 years old with 5 samples: 2 England, Ireland, Scotland and Czech Republic.
H47* Group B (T131C, A16246t, T16362C) several hundred years old, 4 samples: 2 Sicily, Italy, Russia.


H48 (G11016A), estimated to be about 3000 years old.
H48 has 14 samples: 4 from England, 3 from Germany, and 1 each from Ireland, France, Denmark, Netherlands, and Croatia. H48 probably originated in an early Germanic tribe in northern Europe.