For obvious reasons, when producing a descendant report, we often want to exclude living people, or at least hide their details. FTM does, in a way, provide an internal way of doing this. You merely privatize your tree by clicking on File > Privatize. This hides personal details of whoever the system determines might be living (this is reversible using the same setting so nothing will be lost, but you should avoid syncing your tree while it's privatized in FTM because it can screw up your online tree).
Unfortunately, FTM doesn't do a very good job of this. In my experience, it wants to mark anyone born after 1895 without a death fact as "living", even though it's highly unlikely anyone would ever live to be 120 years old. This is contrary to the online tree, which marks people as living if they were born within 100 years and have no death data input, a much more sensible criteria, if you ask me.
1. Go to File > Export. This brings up a window that allows you to select which individuals you want to include in the export, so choose "Selected Individuals", shown right.
2. This brings up the window where you can choose who you want to include or exclude, shown below.
3. Now click "Filter OUT" this time and exclude anyone who doesn't have a death fact. You do this by selecting "Death" in the first drop down menu, then "Any data" in the bottom one, and then "does not exist". You now have a list of people born after 1915 who are deceased (ie, who have a death fact).
4. Now click "Filter In" again, and include everyone who was born before 1915 by selecting "Birth", "Date", "is before", and type 1915 into the text field.
You can now export your tree with this list of people, which should include everyone except those born after 1915 with no death data. Save the file with a new name, so as not to overwrite your original tree. I call mine "Descendant Reports Tree" plus the date. Once exported (and I would not include media when exporting since you're only doing this for the sake of text reports), you can open the new file and now you have a tree that doesn't contain anyone born after 1915 who might still be alive. You can create reports from this tree without any fear of anyone living showing up. Yes, it does mean that you have to do this every time you want to update a descendant report, but it's the only way I have found to create a descendant report with a sensible or customized cut off point for living people.