Hermann married in Liverpool in 1854.  He is assumed to be related to the other Liverpool Dittmers.

DOB and parents shown on marriage record

1871 Census records has him age 26 (born about 1845) from Hanover.
1881 Aged 36, at 45 Ascot St
1891 Aged 46, at 45 Ascot St

Name is confirmed on declaration of Doris's brith certificate, which also shows both spellings of Dittmer/Dettmer.

Marriage record has his full name as Johann Heinrich C Dittmer.

Cannot be the Johann Heinrich Dettmer, born 27 AUG 1847 in Wolthausen, Hannover, Preussen as he married Marie Dorothee Alwine Meine on 02 APR 1875 at Winsen, Schleswig-Holstein, Preussen.

Deaths Sep 1912   (50%)
DITTMER  John H C  67  Toxteth Park  8b 192

There's another John Henry Dittmer who died in 1902. This other John Henry Dittmer was born in Hamburg and lived in Kirkdale.
Deaths Dec 1902   (>99%)
Dittmer  John Henry  51  W. Derby  8b 262

Just a guess !

Probably a similar age to Henry, and still living in Diersbuttle in 1901

b 1867-8 in Hanover, Germany according to 1891 census, and also recorded as a "Nat. Brit. Subj."

Aged  23 in Apr-1891 so must have been born after April 1867.

Aged 24 when he married Freda, 28-Feb-1892, but his father was already deceased.  Mum also remebers that the family came from Hanover.

Aged 42 on 1911 census (and Freda 41)

The probate records his name as "DITTMER Peter Henry" and his Naturalisation Certificate "Johann Peter Heinrich Dittmer". His nationalisation application (in the National Archive, Kew), also records his DOB as 17 Aug 1867, place of birth as Diersbuttel, as well as other information about perents etc. He submitted his birth certificate (issued 11 Aug 1886), so this information must have been verified.  He must have applied for a new birth certificate from Amelinghausen to leave Germany, aged 19
.
DOB: 17 Aug 1867 (and of German parents)
Place of Birth: Diersbuttel, Amelinghausen, Hanover, Germany
Full Name: Johann Peter Heinrich DITTMER
Fathers Name: Johann Heinrich DITTMER
Mothers Name: Katherian Marie Magdalene KUHLMAUN

1939 register confirms DOB as 17 Aug 1867.

Mum recalls he went to stay with relatives, and died in Belmont Hospital, Liverpool.  He is buried with Freda in Landican cemetery (see references for picture).

The death certificate records Henry's place of death as 42 Belmont Road, Walton.  This was the West Derby Union Workhouse until 1865 which then became Poor Law Institution.  In the 1930's it bacame Belmont Road Hospital run by Liverpool Corporation.  In 1948 it bacame Newsham General Hospital, run by the Ministry of Health.

The probate record shows he was living at 34 Bankburn Road, Tuebrook, Liverpool 13 before he was admitted to hospital.

See the following link for further details:
http://www.institutions.org.uk/workhouses/england/lancs/West_Derby_workhouse.htm

Headstone Inscription:

In Treasured Memory of
FREDA DOROTHY,
The beloved wife of
HENRY DITTMER
Passed away 20th October 1939
Aged 69
Peacefully sleeping, resting at last.
Life’s weary trials and troubles are past.
Also Henry, beloved Husband of above
Died 25th January 1950
Aged 82 years

Grave in CoE Section 8, number 820

Death cetificate shows Henry was of 37 Devonshire Road, Upton.  Henry was retired Corporation Labourer.  The death was reported by his son H Dittmer (i.e.Harry) on 26th Jan 1850.  The registrar was Jamie Jones.

The probate records reveal much more information. 
The record text is as follows:
DITTMER Peter Henry otherwise Henry of 34 Bankburn-road Tuebrook Liverpool 13 died 25 January 1950 at 42 Belmont-road Liverpool 6 Probate Liverpool 30 July to Harry Dittmer (the elder) engineer. Effects £231 15s 9d.

Henry wrote his will 18-Oct-1948, only 15 months before he died. Perhaps he was terminally ill then!  A copy of the will was obtailed from the Leeds Probate Office be me 14-July-2012.