Age
We don’t know what age Mr. Gardiner is, though he’s the same generation as Mrs. Bennet and married to a woman somewhat younger.
Family and Situation
Edward Gardiner is the brother of Mrs. Bennet and Mrs. Phillips, which means he would have grown up in Meryton as the son of Mr. Gardiner Senior. Whether he is the eldest (or only) son is unclear, though we do know he did not stay in Meryton and did not inherit the family business (instead, it went to Mr. Gardiner senior's clerk and son-in-law, Mr. Phillips).
Edward is married to Mrs. M. Gardiner, who is originally from Derbyshire, which means that he likely met her in town once they had both relocated or while traveling in the North, presumably after he established his London business. Together they have four children. The narrator tells us that Mr. Gardiner “is settled in London in a respectable line of trade” and that he and his wife live in Gracechurch Street, which would have put them in London proper.
Other Connections
When addressing the crisis with Lydia, Mr. Gardiner consults with professionals named Haggerstone and Mr. Stone on what seems to be legal or financial issues, suggesting that he has a fairly well-educated circle of acquaintance.
Appearance
We don’t know that Edward Gardiner looks like, though we can guess that he vaguely resembles Mrs. Bennet, who we are told was quite attractive in her youth. At Pemberley, Lizzy thinks Darcy has mistaken her relatives for “people of fashion," suggesting that if nothing else, Uncle Gardiner is fairly well put together.
Character
The narrator tells us that Mr. Gardiner is “a sensible, gentlemanlike man, greatly superior to his sister, as well by nature as education” and that “The Netherfield ladies would have had difficulty in believing that a man who lived by trade, and within view of his own warehouses, could have been so well-bred and agreeable.” We do know that Lizzyis actually proud to name the Gardiners as her relatives, and that she seems quite close to both of them, suggesting they have sense and wit. Darcy ultimately ends up being fond of them as well.
Habits and Hobbies
At Pemberley, we learn that Mr. Gardiner "was very fond of fishing...though seldom able to indulge the taste." Later on the trip, he makes plans to fish with Fitzwilliam Darcy and some of the other men of the visiting party, presumably including Charles Bingley.
