7 months is plenty old to make the transition from leash training to ecollar.

If the dog has learned the commands and refuses to obey, he gets corrected. Doesnt mean that every correction has to be a shock, or a "nick". But he should be reminded who's the boss, I put collars on dogs after 12 weeks or so. 21 weeks is plenty old enough. I dont use a beeper function, I give the dog ample time to correct himself before he gets a verbal warning and then he gets ironed out with ecollar. Low stim for my labs doesnt even get a reaction, so they go right to medium, before med-high, then High.