Hi lesleyhannah,
As Valda so rightly points out, both the entries are christening entries, not birth entries, so the year of birth is just conjecture.
*Mary <Bowes>, bap 28 Aug 1803, Scarborough,Bts, ,Yorkshire, parents George Bowes and Elizabeth.
This is one of those infuriating christening batches (either 'C' as in this case, or 'I') which have relatively recently come into the IGI and which give no information whatsoever about their source! And I'm not all that confident about them as I found a place name for one such batch which was completely wrong - obviously the place (parish and county) had been entered incorrectly on the first entry and then just "filled down" through the whole batch!
*Mary Merry BOWES, bap 2 Aug 1808, Scalby near Scarborough, mother Bridget BOWES
This one does give its source - and the film notes in the Family History Library catalogue on FamilySearch seem to indicate that it is the Register of the Parish Church of 'Scalby (near Scarborough)', Bishop's Transcripts.
One or neither of these could be the Mary who married Edmund MALTBY.
Mary Merry sounded a strange combination of forenames to me but a search on FreeBMD for all event, just enter forenames Mary Merry, actually came up with some hits...
Given Mary's age of 47 in the 1851 census, it seems very likely that she would have married before the start of statutory registration - supported if the children in the 1851 census are Mary's (as well as Edmund's) also from their ages (which range from 17 down to 7).
Sad to say, it looks as though Mary might be a brick wall unless you are fortunate enough to come across the marriage entry in a church register which has not been entered into the IGI - and even then it might not have anything to give a clue to her birth.
JAP