My mil let my LO tried lemon. In general we let her do what she wants since she hardly get to see the LO plus she is a nurse. When I told my mum, she reprimanded me and said it would cause gastric. Would it?

Yes it's ok. And wld recommend you to let baby try as speaking from my own experience. My hub has always been very conservative in terms of parenting. My son has suddenly grew to dislike eating fruits at 1 year old. He would not eat any kind of fruits be it that he has tasted or not before. He's currently 18 mths old.