You have to be careful here, quite a few veterans claimed to be Chelsea Pensioners when they weren't To qualify for the pension you needed to have completed 20 years service meaning he would have joined as a boy however, as in the case of my GGG Grandfather, if they serves at Waterloo or were a part of the Army of Occupation thereafter, they were awarded extra years of service.
I've had a look on the Forces War Records site and the Waterloo Medal Roll and there are a number of John Bailey's, your best bet would be to start there and whittle them down.
I've also had a look on Find My Past under their Chelsea Pensioners section, there is a John Bailey born 1791 Boston Lincs if that's any use?
David