The oldest Dal on record who won championships for his obedience was 10 years old when trained. If a 10 year old Dalmatian can be taught new tricks then so can a younger one.
Dalmatians are very intelligent, but they also want to please.
You must show your Dal who is in charge. Be ready to lavish praise for a job well done. This is especially important for rescued Dals. They need positive reinforcement. They don't respond well to negative reinforcement.