Depends what you mean by "jamming" I guess.
For some musicians, "jamming" is synonymous with "improvisation." That definition of "jamming" is dependent on training your ear. A lot of musicians have a great ear at 17 months, but for others, it is slower going. I personally used to be "tone deaf" and it took me a few years before I was comfortable improvising unfamiliar songs on a public stage (not that it ever stopped me from
trying in the privacy of the garage or rehearsal studio). For this type of "jamming," it helps to have a good grasp of music theory and to be familiar with popular chord progressions (such as I-IV-V, I-V-vi-IV, 12-bar blues, etc.) in all 12 keys.
Another definition of "jamming" means "getting together in a casual environment with other musicians and playing songs we all know." Assuming that you know some popular songs (or else you know how to learn songs on the spot, for example by hearing the chord progression or sight-reading a chord chart) then there is no reason why you can't "jam" at 17 months. You've been playing for about 70 weeks; about how many songs do you typically learn per week? Even if you learn just one song per week, that is a repertoire of 70 songs. Unless you are studying some obscure and unpopular genre, you ought to be able to find some musician buddies who know 10 or 20 of those same songs and can "jam" (i.e. casual group music-making) with you.
I started playing with other musicians from day one. For me, that is what music is all about. I feel that I progressed much quicker by playing together with other musicians. We learned some very easy songs together (classic rock type stuff), and even wrote a few original songs of our own!