Is it true that anybody can become a yogi if he really tries?What do you mean by really? If you mean sincerely, then certainly anybody can become a yogi.
Yoga means union with God. A yogi is he who is one with God. Sooner or later, all human beings will realise God. But the person who takes to Yoga reaches God sooner. If you yourself want to become a yogini and realise God, then right now start praying. Especially if you want to reach God before the rest of humanity, please do not delay.
Now, how do you go about praying? If you pray to God for candy today, tomorrow you will ask Him for ice cream and the day after tomorrow for something else. And God will give you everything that you want, except Himself. But if you pray to God only for Himself and nothing else, He will give you all that He has and all that He is. In getting all that He has and all that He is, not only will you get your candy and ice cream and everything else that you wanted, but you will also get things that you had never imagined, things of an infinite nature. So pray to God every day to give you what you need and not what you want. Then He will give you what you actually need to become one with Him.