I was 19 when my son was born and he has been breastfeeding for 14 months now (yes, he was my first).
I'll be tandem nursing both babies if Jericho doesn't wean by then.
The KEY is to spend as much time with your baby as possible.. lots of skin to skin contact.. and offer the breast whenever your baby is fussy.
As soon as they get a bottle, you will start to lose your supply.. they have to nurse for you to make milk.
For example: Jericho would nurse for 5 minutes - an HOUR at a time the first few weeks, and I let him nurse constantly.. so after the first couple months, I never had to worry about supply.
It does take some effort, and you need A LOT of support and correct information.. but it is SO totally worth it and I'd breastfeed 10 more if I had to. It's wonderful and beneficial for baby AND mommy (decreases your risk of breast cancer, helps your uterus shrink back to normal size, etc.).
Good luck!