Team Scotland's Ross Murdoch received the note after it was delivered to his parents' home, despite being addressed simply to "Ross Murdoch, Commonwealth Champion, Balloch".
The 20-year-old called on his Twitter followers to help him trace the youngster to show him where he trains.
The young fan was later identified as Brian Fitzpatrick, from Dumbarton, West Dunbartonshire, whose mother Claire told the BBC: "He loves swimming and is very excited at the prospect of meeting with Ross."
Gold medal winner Murdoch wrote on Twitter earlier: "RT&help me find 5yo Brian who sent me this amazing letter! I'd love to meet him and show him around where I train :-)".
He previously thanked Royal Mail for ensuring the letter reached him.
On August 11 he wrote: "Parents received some fan mail today. Great @RoyalMail for getting it to the proper destination! Cute GoodJob"
Murdoch secured a gold medal in the 200m breaststroke at Glasgow 2014, to which he later added a bronze in the 100m breaststroke.