The pilot course duration can vary depending on your previous flying experience. If you already have a Private Pilot Licence (PPL) your duration of pilot training becomes shorter compared to students who start fresh after 12th standard. This is because a PPL holder has already completed part of the pilot study duration.
A PPL allows you to log flight hours practice essential flying skills and cover theoretical basics. When you upgrade to a Commercial Pilot Licence (CPL) the pilot duration required for flight training reduces because those PPL hours are counted. In many cases students save 6–8 months of training depending on their flying school and country regulations.
When we talk about how many years pilot study duration takes internationally the course duration of pilot training is usually between 18 months to 3 years. In the USA or Canada for example students can finish faster due to flexible flying conditions. In India the duration to become a pilot is generally 2–3 years depending on weather DGCA exams and aircraft availability.
For fresh students after 12th the pilot course duration after 12th is typically longer since they start from zero hours. But with a PPL you already cover part of the pilot study course duration making the course duration for pilot licensing shorter.
After CPL if you aim to become an airline pilot additional training and typerating are required. This adds to the airline pilot course duration but overall a PPL holder always has an advantage in terms of pilot license duration and faster progression.
Yes holding a PPL shortens the duration of pilot training course reduces costs and helps you complete the pilot duration of study quicker to become an airline pilot.