Hi thewill,
All soft materials will form some impressions to some degree over time but latex is less likely to soften and form significant impressions than other types of foam.
There isn’t a way to assign a number of years to the life of a mattress because there are so many variables involved not the least of which is the person themselves but post #4 here and the posts it links to will give you a good idea of the factors that are involved in the relative durability and useful life of a mattress.
Both 100% natural Dunlop and blended Talalay have a long history of lasting decades in some cases … particularly with firmer versions (see the video here for an example) and latex is one of the few materials that you can reasonably expect to maintain its comfort and support for the length of a warranty period and often beyond.
Phoenix