In the 1841 census he says he is 50. Adults' ages in 1841 were supposed to be rounded down to the nearest 5 years, so he could have been born any time from 8 June 1786 to 7 June 1791.
In 1861 he says he is 73, and in 1871 83, which is consistent and if accurate means that he was born between about April 1787 and March 1788 (because the census was taken at the end of March or beginning of April).
The index at
www.scotlandspeople.gov.uk lists 25 James Drummonds born 1786-1790. Only 21 of these baptism records include the mother's maiden surname. None of the baptisms was in either Kinross or Falkirk. (Where did you find the ones you mention above?)
The post-1855 statutory deaths index lists just 8 James Drummonds born 1788 plus or minus 3 years
There are only two deaths in the index of James Drummonds born 1788 plus or minus three years that can be matched with any of the baptisms:
Mother Duncanson, baptism Logie 1787, died Edinburgh 1872
Mother Ritchie, baptism Forgandenny 1788, died Dunbarney 1875
There are two deaths with no mother's surname
Tillicoultry, 1855, aged 67
Polmont, 1867, aged 80; could be the one baptised in Polmont, 1787, mother's surname Gaff
It may be that the actual death certificates would contain information that would enable them to be indentified with certainty.
And there are four deaths with mother's surname not matching any of the baptisms
Mother McKinnon, Kilmore and Kilbride (Argyll), 1859, aged 66 - if age is accurate, born 1792/1793.
Mother Kesson, Hutchesontown (Glasgow), 1859, aged 68 - this is probably the one baptised in Paisley in 1791
Mother Gairdner, Blackford, 1874, aged 88 - probably the one baptised in Muthill in 1793
Mother Black, Portmoak, 1876, aged 85 - probably the one baptised in Portmoak in 1791
If so all are too young to be confused with your James Drummond.
The index to the 1851 census at
www.scotlandspeople.gov.uk lists 10 James Drummonds aged 60 to 64.
Age 63, Polmont - born Polmont so probably the one who died in Polmont in 1867
Age 60, Portmoak - born Portmoak so probably the one who died in Portmoak in 1876
Age 60, Cambuslang - born Cambuslang but too young to be confused with yours
Age 62, Dunbarney - born Forgandenny so probably the one who died in Dunbarney in 1875
Age 60, Crieff - born Crieff but possibly too young to be confused with yours
Age 60, Old Kilpatrick - born Old Kilpatrick but possibly too young to be confused with yours
Age 61, Neilston - born Ireland
Age 64, Edinburgh - born Logie, Clackmannanshire so probably the one who died in Edinburgh in 1872
Age 62, Tillicoultry - born Dunning so probably the one baptised in Dunning in 1786 and died in Tillicoultry in 1855
Age 63, Dunblane - born Dunblane so probably the one baptised in Dunblane in 1787
So that leaves 23 baptised in 1786-1790 and not accounted for
Mother Clerk, 1786, Muthill
Mother Donaldson, 1786, Comrie
Mother Irvine, 1787, Shapinsay
Mother Smith, 1787, Sanday
Mother Bishop. 1787, St Cuthbert's (Edinburgh)
Mother Burn, 1788, St Cuthbert's
Mother Whyt, 1788, Portmoak
Mother Buchanan, 1788, Kilmadock
Mother Drummond, 1788, Monzie - but the same parents had another James in 1789 so this one probably died in infancy
Mother Watson, 1788, Dalkeith
Mother Martin, 1788, Larbert
Mother Drummond, 1788, Comrie
Mother Drummond, 1789, Monzie
Mother McRobbie, 1789, Muthill
Mother Wallace, 1790, Durisdeer
Mother Ross, 1790, St Andrews and St Leonards
Mother Millar, 1790, St Ninians (Stirling)
Mother Maxton, 1790, Crieff
And with no mother named:
1786, Dunning
1787, Inverarity
1787, Dunblane
1789, Methven
Why not make a spreadsheet and see if you can match up any more? And take a look at the 1841 census and add that information? There is a reliable census transcription at FreeCEN
https://freecen1.freecen.org.uk/cgi/search.pl that is almost complete for Scotland for 1841 - only a few parishes in Perthshire and a few in Berwickshire are still to be added.
