I took my first attempt in jee main got 100 marks in 2017 then 2018 I really wanta go for the third time I feel like 156 is not my full potential will it be OK and my age won't matter cuzz it a little bit less

See 156 is good score in iit jee mains and definitely u will good college . So no need to go third time because even next year there is no surity whether u will good marks or not. Many factors r there who those effect the performance .so u take NIT and performe there very well.