If you use the search box on the side of that page for "zong" it will bring up 10 results from The Jamaica Gleaner.
As for finding out more information about either Collingwood or Kelsall, then the most likely places to look are in merchant shipping records. Most of these are held at the National Maritime Museum in London (Caird Library): http://www.nmm.ac.uk/researchers/http://www.nmm.ac.uk/researchers/ You will need to apply for a reader's ticket for the Caird Library, and double check availablity of sources as a little while ago I was aware that they were moving some of their collections off site. I have been to the Caird Library, but found it difficult to navigate the records held there, although I was focused more particularly on other surnames at the time.
Another place to look would be in Liverpool, they may have kept their own records from the period. Liverpool certainly devotes museum space to their part as a major port. The Museums of Liverpool website: http://www.liverpoolmuseums.org.uk/ourmuseums/http://www.liverpoolmuseums.org.uk/ourmuseums/ lists two likely sources - The Merseyside Maritime Museum and International Slavery Museum.
Maritime records may give age or date of birth (with any luck).
For James Kelsall (1st Mate), I would expect to see a few previous voyages as either 1st/2nd/3rd Mate (depending on how desperate they were for crew).
Luke Collingwood had never commanded a ship before, The Zong was to be his first and last time. He had previously served as Ship's Surgeon on at least one other voyage. He commanded The Zong in the hopes to make enough money for retirement, so one would gather he was around 40-55 years old at the time of the voyage. (The estimated birth for him would be 1726-1741, with my guess that he would likely be in his late 40s, perhaps 48 so about 1733 being the estimate.)
Luke Collingwood, it appears, did go back as a general practitioner after The Zong. There is, what is likely to be a posthumous entry for him in a Directory (most likely a Liverpool Town Directory) of 1784 as "surgeon, medicine". I only have the transcription via Ancestry.
Luke Collingwood was married, and had at least four children who were born in Liverpool. I have not been able to find out to whom he was married, or when, but the estimated time of his marriage would be the early-mid 1760s.
Be warned that the Northumberland Collingwoods did have a practice of naming Lukes, but he is not necessarily of that line, as there are Collingwoods scattered all over England, and records are very patchy during this period. The most famous of the Northumberland Collingwoods is Lord Admiral Cuthbert Collingwood. My Collingwood ancestor was apparently the first Collingwood to go into the Royal Navy, and we are supposedly related to the Northumberland line but that remains unproven. Also be aware that there are some very fanciful Collingwood pedigrees floating about online that should be viewed with extreme caution.
Getting back to The Zong voyage, it was clear that the captain and likely some or most of the crew, were not hugely experienced. The middle passage of that voyage took double the usual time.
Anyway, I hope the above is helpful to Zong researchers present and future.