I said realistic penalty. I.e. do they pursue and prosecute it. Oh, and I know how to use a long bow, despite being an American... I took archery in high school.
As far as selective service...
From wikipedia:
As an alternative method of encouraging registration, federal legislators passed laws requiring that to receive financial aid, federal grants and loans, certain government benefits, eligibility for most federal employment, and (if the person is an immigrant) eligibility for citizenship, a young man had to be registered (or had to have been registered, if they are over 26 but were required to register between 18 and 26) with Selective Service. Those who were required to register, but failed to do so before they turn 26, are no longer allowed to register, and thus may be permanently barred from federal jobs and other benefits, unless they can show to the Selective Service that their failure was not knowing and willful.[6] There is a procedure to provide an "information letter" by the SSS for those in these situations, for example recent citizens who entered the US after their 26th birthday.[28]
Most states, as well as the District of Columbia, Guam, Northern Mariana Islands, and Virgin Islands, have passed laws requiring registration for men 18–25 to be eligible for programs that vary on a per-jurisdiction basis but typically include driver's licenses, state-funded higher education benefits, and state government jobs.[29] Alaska also requires registration to receive an Alaska Permanent Fund dividend.[29] Eight states (Connecticut, Indiana, Nebraska, Oregon, Pennsylvania, Vermont, Washington, and Wyoming) as well as Puerto Rico have no such requirements, though Indiana does give men 18–25 the option of registering with Selective Service when obtaining a drivers license or an identification card.[29] The New York State Department of Motor Vehicles automatically registers young men 18-25 with the Selective Service as federally required, whenever they apply for driver licenses, learner permits, or non-driver identification cards.[30]