It is a long 5-7 months waiting for eggs if you start with chicks. And chicks are fragile, it is not uncommon for some to die. There will be people on this website that will say they have never lost a new chick, but plenty have, me included. However, With a box, a heat lamp, a chick feeder and waterer, you are pretty much set up, and they will grow. If you are raising the chicks you will need a heat source of a couple of weeks.
Another question you need to look at, is what kind of set up do you have for when the birds are full grown. One does want to make sure that it is predator proof, and usually people, (me included) find out the hard way, that it is not quite as predator proof as one thought.
If I could find someone with even a bit older hens, that is where I would start. Then each year, add chicks..... that is called chicken math, and you will think you are immune, until..... spring comes, and there are chicks.
Older hens, unless in a rescue situation, or obviously sick with runny noses, or lice or mites,...... DON't take anything that does not look healthy..... if you think it looks unhealthy, it probably is.... but anyway, older hens are a bit more sturdy to start out with, and you get eggs right away which is always fun. However, if you start with chicks, it is fun too.
Either way will work, it is a fun hobby, but we all have had a wreck or two, it is not fool proof. And as Ridgerunner often mentions, they are living animals, and there is no 100% answer. I have learned a lot here on this website, and some trial and error.
Mrs K