Champagne experiences three stages of ageing. The first ageing period when the Vin clair/ground wine ages is not really what interests us, just if the vin clair undergoes the malolactic fermentation and if it has contact with wood or in stainlesssteel as these are factors which define the taste and the richness of the champagne.
The second ageing period begins with the second fermentation, yeast and sugar are added to the vin clair or the blend of vin clairs inducing the fermetation which gives us the bubbels. The yeast dies and sinks to the bottom of the bottle. What now occurs is called autolyse. This is the process where aromas typical to champagne develop, yeasty, brioche and biscuit notes. Autolyse needs at least 18 months for the aforementioned aromas to develop. The longer the contact with the dead yeasts takes place ,the complexer the aromas get. The regulations of non vintage champagnes say the yeast must remain in the bottle for a minimum of 12 months, most producers store the bottles longer. For vintage champagnes the required ageing is 36 months, again most producer do a longer ageing period.
After 5 years it seems the autolyse is exhausted and the aromas developed at this time define the champagne.
The second fermentation with some exceptions take place with metal caps, this prevents contact with oxygen. Newly degorged bottles for this reason even after 5 to 10 years taste fresh and reductive directlyafter degorgement.
The third ageing process occurs after the degorgement, with the removal of the lees, the addage of the dosage sugar is introduced into the champagne and the cork. This kicks off the maillard reaction where amino acids released from the lees during autolyse react with the sugar developing toasty, full bodied aromas. For this reason it is important after degorgement to store the bottles for at least 6 months so that the champagne finds its balance and that these aromas develop. Through
the cork the champagne now has contact with oxygen which induces the next ageing process exactly as it does with wine. Even basic entry level champagnes profit from one or two years ageing.
Are there rules to ageing, I personally do not think so. Personal taste and the cellar one has are the most important factors. For some people a chamapgne cannot be old enough for others they value the freshness. What is importing for ageing is the dosage and the age of the vines. Extra Brut (under 3g/l) or Non Dosage lacking sugar are in my opinion better drunk on the younger side as their freshness is the appealing factor, an exception must be made for grapes which were harvested ripe meaning they have more natural sugars from the beginning and the necessary substance for ageing. Old vines produce small grapes, where the juice is more concentrated, similiat to burgundy these longer ageing to reveal their true potential.
I personally am not a fan of late degorged champagnes such as Bollingers RD or Dom Perignons Plenitude ranges. When these bottles are opened the freshness is to begin with obvious but after a year they tend to age quicker than the normal degorged champagnes. But as with all things to do with taste, it comes down to the individual taste and ultimately there are no rights or wrongs.