Hate to say it but there are 2 or 3 topics like this already on this page.......
But anyway, if you're riding a bike that hurts your back then change the set up, you've only got one back and you sure as hell don't want to mess it up whilst you're young. So man up...... erm no, not a good idea.
But as has been said, type of bike is personal preference, adjust the set up of your bike to suit you accordingly, be if frame length (reach more importantly) stem length, bar height etc. I'm a short ass that rides a long stock and I've got lanky friends that ride long mods.