Can I do pilot training courses even after age 26 ?
As far as I know there are no maximum age restrictions on getting a pilots license anywhere in the world. Many countries have a minimum age restriction for getting a license, that usually does not prevent pilot training from taking place. 26 is fine, in fact 76 is fine as long as you pass whatever medical is required.
To expand a bit on @GdD's answer, a number of aeronautical regulatory bodies, including the FAA, do not specify a maximum age for flight training or executing the privileges of Pilot-In-Command under most circumstances; as long as you hold a valid medical, you're in the clear.
That said, your individual circumstances may be different. There are some exceptions to this even in the civilian world, such as maximum age limits when flying for certain airlines (such as the age 65 rule for Part 121 operations in the US). If you're in a part of the world where airlines offer cadet programs and such, they may also impose maximum age limits for applicants.
If you're interested in military flying, the armed services may also have additional restrictions on maximum age for flight training; the USAF for example, had the age of 26 as the upper bound for anyone applying for a pilot slot about 5-6 years ago, and armed forces the world over have similar restrictions in place.
Thanks to @SSumner for providing a link with the current age limits for US military pilot training.
It would help if you specify if you are getting the license to fly private or commercially. For private there is no age restriction if you pass your medical, as is the same for commercial. However as mentioned some airlines may prevent you from flying after a certain time. That all being said this video brings up some good points about starting training later in life (in your 30's). It takes a lot of hours to become a commercial pilot and the later you start training the later you enter the workforce (as with any job). I would think 26 is perfectly fine. Im getting my Private Pilot and started at 23. There are plenty of people at the flight school well over 50 starting their training as well.