From what the Wiki told me, it won't work with catapults, as they have a minimum range. Ballistae don't.
Minimum range? Indeed, it does. Never noticed that. (Probably because my catapults are rarely used in anger.) Good job most of my actual defensive catapults (not really there for more than basic pestering duty, on most maps) usually cover a much longer inward road than that[1], or they'd be absolutely useless.
But I don't think (and it doesn't mention it) that this affects training, if you had a catapult throwing exactly one tile until a wall (the typical training setup, sometimes I set it up so it has an attack direction and a perpendicular/opposite direction training direction). And with a stone-conveying system they're usually travelling a long way, regardless.
Seeing as you can use like three bolts over and over, why not?
I'd wait until you can get really good quality bolts made, and chuck stones before the appropriate craftsdwarfs have the necessary skills and are just training up on other items. Get your weaponsmith (I think they're the one who help with the arrow-heads made) trained up on the copious amount of weapons you're going to want to make on the way to equipping your army-in-waiting.
Unless you're training them up on arrow-heads before making your
real weapons. That'd be an alternate plan, especially if you're expecting to loose (and, in the process, lose) a lot of ammo in your first real attack/defence.
[1] As it is, I always have at least 10 tiles of unfloored gap between the fortification-covered siege-engine exit and the same-Z roadway they're covering, and the (usually underground) path leading up to there is often most of the distance to the edge of the map, with a stone-catching channel all around with locked access in case I want the stones back, or to attack anybody having also fallen off the roadway. But that way, the three-or-so stepped catapults I have aimed down that route have a good chance of sending stones down while the invading force is still making its way towards me. (And I usually shut off the entrance once they've started their way in, so when I cause them to break they can't escape and I can keep on hitting them, or sending my military in for a bit of R&R... After stopping any ballistas that are also pointing that way, of course.
)