Interesting proposal, but I recommend having the years be calculated as integers (or perhaps half-years).  Floating rewards based as a function of difficulty _and_ day-to-day age combines to a very random mining scheme that would greatly favor pool-hopping.

The mining proposal method may also be seen as an inflationary coin until years in the future; as more people mine the coin, difficulty increases, pumping out even more coins.  This could cause a massive inflationary spiral for the first year or two.  Maybe it would be better to base "coin age" not from years of first block, but from number of blocks generated.  This would be pretty easy to back-calculate into years, based on the 1 minute per block target.