As tasting samples, I find the very young ports quite interesting, but would I want to tackle a whole bottle? - not really, I am a bit too tannin-averse for that.
After the initial flush of youth, the wines mostly go through a dumb or 'closed' phase, when they are flat and unexpressive, but very tannic still. Those of a chocolatey nature seem a little more approachable during this phase.
Then there is the teenage 'Kevin' phase, when the wines begin to emerge as adults, but lack composure. The '91's were notorious for this, but now seem to be growing out of it, whereas a recent encounter with a Cockburn '94 (a wine that I re-visit roughly once a year) showed the characteristic for the first time.
After about 18 years there is a great divergence of maturation between different wines of the same vintage, and of wines from different vintages. In the worst cases, wines can sometimes appear to be over the hill at that age, while others can still seem immature twenty years later.
Another characteristic, one that I associate with the '77 vintage in particular, is what I term the 'Peter Pan' problem - a wine that shows signs of growing old, before it grows up - showing loss of colour and problems with integration, while the tannins are still quite harsh.
Setting aside any infanticidal tendencies you may have..
I would suggest the best way to determine the optimal drinking windows for the stock in your cellar is to leave them in their cases until they are about 16-20 years old, and then take them out of their cases and into a rack, selecting the weakest bottle as you do so. From that bottle, and your own personal preferences, you can determine whether the wine is good current drinking, needs a few more years - or needs loads more time.. - and re-visit accordingly.
Tom
I may be drunk, Miss, but in the morning I shall be sober and you will still be ugly - W.S. Churchill