I am waiting for my BigY results and hope they will provide some useful information (as I do not even know the forming age of R-YP3994, though the TMRCA should not exceed 2400 ybp).
The "formed age" of a clade is always the TMRCA of the one it descends from. So in this case, the formed age of R-YP3994 should be ~2400 ybp (the TMRCA of R-Y2902). It's nice that you have ordered the BigY. You will get a TMRCA estimate with the Italian from Palermo, which should be less than ~2400 ybp. However, I'm not sure how many other BigY/NGS tests currently there is for R-YP3994. It's possible some of the others on FTDNA only tested YP3994+ through a SNP Pack. There should be at least one more since it takes two NGS tests to form a subclade, so perhaps the second one chose to hide his sample on YFull.