If you can afford it.
My info is dated, but I was one scrawny SOB as an ENS/JG. I think I weighed a buck thirty soaking wet as an ENS. I could pound weight-gainer shakes and lift, and absolutely nothing would happen (oh, to have that metabolism back).
That said, all I remember doing was signing a waiver in the API building saying more JAG-like words to the effect of "the Navy bears no responsibility for the spinal fractures your scrawny ass will get in the event of an ejection." I have 700+ hours in an ejection seat that I was probably too light for the majority of the time; I know on Das Boot (with no beer), I was consistently below 140.
Is this a new thing that Big Navy is being this anal about seat weights? Maybe I was just on the right side of the weight curve, but I don't remember this ever being an issue when I was a stud.