The longest I've had wine in the bottle is 10 years.
Aging (bulk or bottle) doesn't add flavor. It provides the time necessary for the wine to transform as it goes through normal chemical changes.
When to bottle is a trade-off. It's better if the wine has sufficient time in bulk for the wine to get through the initial chemical changes as a whole. IME, that timeframe is 4 to 12 months, and it depends on the wine. Whites and light fruits generally need less time, as there's less "stuff" that is going through changes. Heavier whites and light reds need more time, and heavy reds need the most. In general, the higher the body level, the more time is beneficial.
Beyond a year? Unless the wine is being barrel aged, I don't know if there is a benefit to bulk aging. Evaporation occurs through the wood, so barrel aging continually change the wine.
Another advantage of bulk aging is the wine is not being consumed, so it's got the chance to age.
This may sound humorous (and it is!), but it's also true.
Wine ages faster in smaller quantities, so there is an advantage to bottling. Also, the wine is safer in the bottle. Once the cork is in, the wine is sealed, and unless the wine was contaminated, it's as safe as it will ever be.