This is a touch post due to a few reasons. 1, none of us realy know your training intensity or what your diet looks like. 2 Yes you are young, but I know many people who mature by the time they are 19 then have a very hard time gaining any mass. Example my roomate, he is natural, and has been training for 5 years and has only gained 10 lbs. His stats 6'5 195, ripped to the bones, literaly.(hhaha)
I can tell you from personal experiance I waited till i was 19 and weighed 200lbs. At this time I was very anxious and wanted 230 fast. I feel now @20 I should have waited, but if I could do it all over again i would have started cycling...lol
I guess what im trying to tell you is what Ranger A mod on the board(whut up BRO)told me a few years back, you and only you will know when the time is right.
Hope this helps