Yes of course you can veg them. Youll need to root the cuttings in the Veg state, then its totally your choice when to flower them. Grow them to whatever size suits your grow room.
Your mate was talking about growing SOG style, where often hundreds of newly rooted clones are packed tight together and flowered immediately after rooting with no veg time. This creates a huge even canopy of top colas (giving the optimum effeciency in your lighting and space etc for maximum yeild) But growing like this is going to be a hell of alot of work. Also if you get caught growing in this way I would imagine it's going to be harder to justify as being for personal use. This is pretty much the method that commercial growers use but it can be scaled down, but it's hard work.