How does teak age over time?
Like all natural materials, teak is affected by the environment and it will age according to the conditions that it is kept in.
The most harmful of the environmental factors is usually the amount of direct sunlight. Teak is more durable to sunlight than most timber species but direct sunlight will still degrade teak over time. Even without protection like a UV protective varnish, it will still take many years or even decades for direct sunlight to seriously degrade teak. The most obvious change will be the change in colour from its natural golden brown colour to a grey over time.
The good news with this colour change is that it is only superficial and with some sandpaper and some elbow grease you can generally sand through the grey and get back to its natural golden hues.
Aside from sunlight, teak is not very susceptible to degradation. Of course it is possible to get damage from pests but the natural oils in teak make it unappealing to pests in general.
Water is also an issue but once again teak has natural oils to protect it. This along with its high silica content mean that teak is actually very durable in the wet and as long as it is not left to sit submerged, water will basically have little or no discernible damaging effect.