Cannabis is totally harmless?

Hi, i'm here to ask you what you think about cannabis. Most of people can think that is harmless, we seen a lot of researches of Universities that confirm that, butthere are studies that say it can be harmful some times. I think, after reading a study, that after the 17 years it's quite harmless, but when you are younger and use cannabis it can be risky for your memory. That because before the age of 17 youarestill in full body development, and the barin as well. Ican't give you the link of the study because i founded it on instagram time ago in italian, so sorry, but i think you can search it. I have to say that i use cannabis, im 19, i started when i was 15/16. I have some memory issues, but i can't know if the fault is that i started at 15/16 using cannabis, but before i never had those problems.
What you think about it? And if you started using cannabis, when you started?