age discrimination

i live in maryland & worked as a construction worker [fire sprinkler installer] witch was heavy labor screwed my back really bad and alot of my joints through my body i worked 4 8 yeaRS @40 -60 PLUS HOURS AWEEK . i got denied because im 29 yrs old and the form says "due to my age we understand you cant do the same profession" i was maken $25.00hr but im suposed work for min. wage @ $5.00hr, i guess. i never been on here but mabey ill get a reply thanks