They can always try casting by skipping 1 round of prep (with penalty of course). I wouldn't recommend skipping 2 rounds of prep, but I have level 1 casters casting a spell every other round.
To be fair... to be a nuker requires practice, time, experience. I'm sure your armsmen want to be Zorro, Inigo Montoya, Conan at level 1 too... but it just doesn't happen.
The work around we did for a couple of decades was to just start the players at level 5. It gives the GM more options for baddies to send at the party, the party is more resilient, and they are more skilled. Honestly, that's a great compromise. GM's who go to Cons usually have level 5 PCs for players to use as it gives a very robust feeling for the game.