Interesting. While I think giving money to political campaigns
   is generally kinda ridiculous for ANYBODY to do, nevertheless if
   you want your voice heard in some way, you should be allowed.
   Anyway, an interesting side of things I hadn't thought of. It's
   a form of [1]#ageism - theoretically designed to prevent abuse,
   but there's no law in the USA that prevents people under 18 yrs
   old from donating to political causes and getting their name on
   the rosters as supporters, so it's really the choice of the
   candidates ultimately.
   http://youthrights.org/2016/01/19/the-nine-presidential-candidates-who-dont-want-your-support/

References

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   1. https://plus.google.com/s/%23ageism