When dealing with emancipation laws... what statute applies... the current one or the one that was in effect at the time child support was was assigned?

When my support was assigned in 1993 the emancipation statute stated 18 or graduating high school, which ever came first... in 2001 it was changed too 21or emancipation meeting three qualifications. Now as of July 1 this year the 21 will be lowered to 19. Shouldn't the original statute apply since it was valid at time of judgement.