For the Marines, height standards for male applicants range from 58 to 78 inches. Height standards for female applicants range from 58 to 72 inches. The services have both height and weights standards. If you fail the height / weight charts, but pass the body fat standards you are still eligible for service.
Most dogs require 1-2 years to become a service dog and be fully trained in public access skills. The training cost of working with a professional trainer at $150 an hour would be about $7,200 a year.
Some are intentionally bred for service work, some are career change dogs bred for other work, some are rescues, and yes, some started out as pets. However, the odds of any given dog having all the right stuff and actually completing training to become a service dog are about 1 in 100. service dog must receive adequate training in three areas: obedience, tasks, and public access. He should be reliable in obeying commands at least 90% of the time on the first command. He should sit, down, come, stay, and heel properly.