You can learn on a keyboard yes, but if it only has 60-something keys, as opposed to 88, and if it has no pedals, then you won't last long with it. Of course it's far better than nothing at all, but it might not be best for you once you get onto higher grades, because you'll need to start using the pedals, and you'll need to use notes that are too low for a standard keyboard to play....
I've been playing for about half a year and have been using a standard size keyboard, but now I'm upgrading to a Digital Piano.....
There are also full size keyboard which don't cost as much as digital pianos...
And who knows, if you start saving for a piano/full size keyboard now, by the time you come to needing more keys and pedals and stuff you'll have enough money for an upgrade!!
Good luck with learning, hope I was useful
Love Laura
XxX