Because I'm in the UK, and I know there's a difference between sycamore here and sycamore in the States, the tree I'm talking about here is Acer pseudoplatanus. Assuming you don't have a named cultivar of it (Acer pseudoplatanus 'Brilliantissimum' for instance), the life span is 2-300 years in optimum conditions, the roots will only cause a problem if the tree is planted too close to pipes/house foundations, etc., This tree should reach 60 feet, up to 150, sometimes 200 feet high. As for the exposed roots, no, you should not cover those with soil - if you have large roots on top of the soil, I assume the tree is already quite mature.
As for pruning, it should never be pruned in spring, or it will bleed excessively. Lower branches can be removed after June, without getting too close to the main trunk and wounding it, and any hard or heavy pruning is best carried out October-December, when the tree is dormant.
There is no need to fertilize this tree, it's obviously doing very well without any special treatment. I don't know if this is true in the USA, but in Britain, the presence of Acer pseudoplatanus is a cause for loud groaning and general dismay - it produces thousands of winged seeds yearly, and these seeds readily root and grow wherever they land. Perhaps, though, this is not such an issue in the States.