You should really consider your circumstances before worrying about TTC.
I consider myself young (24) to be pregnant with my first. myself and my husband haven't been together all that long in the grand scheme of things (3 years) but 6 months after getting married decided to try for a baby.
I am now pregnant with twins which is absolutely amazing, but in our plan had only budgetted for the 1 baby.
we both have decent jobs that pay relatively well, and we can JUST about afford. I will have to return to work earlier than planned though which devastates both of us.
we have managed to get loads of things second hand and have extremely generous friends and family and have still spent approx £1000 in preparation for babies. We dont have luxury items.
It is so expensive having babies, and being the first of my career-girl friends to have babies I have no clue.
if a baby is what you want then great, but have you seriously considered the costs, the element of surprise and the fact that this ties you down and to your partner for life.
At 17 I was with 'the one'. Or so I thought. 8 years on, and another 'the one' later, I am old enough to realise how ridiculous I was. Im not suggesting you are the same as I was, but Im a fairly sensible person and managed to get it wrong.
Good luck whatever you decide, my main advice is get a pen and pad, tot up costs, consider all outcomes and enjoy being a teenager. 18 is a hell of a lot of fun without children! as is 19, 20, 21.... etc! 