There was a terrible typo in my answer to you. Spell check killled me on this one, Please, Please accept my appologies and re-read this answer! I had no intention of writing the word "Sexual" but rather intended to write "Physical" in the 5th paragraph. Once I re-read what I had posted I was horrified!
Hi, Welcome to JustAnswer! My name is XXXXX XXXXX I will endeavor to answer your question. I am very sorry to say that 25 years old is certainly too old to pick up the game of tennis and hope to make it to the professional level.
Most pro tennis players started when they were young children and practiced hours upon hours every day for years before they even found out if they were good enough to play professionally.
Even for those who do make it into the professional ranks, by the time they make it onto the tour they have been playing for a half or their life at least.
That said, when you realize that the average age of retirement for a professional tennis player is 30 years old, it is then safe to say that there is not enough time at 25 years old for a person to learn the game, practice enough hours to get good enough to make the professional tour and then not be well past the age of retirement.
My recommendation to you however, would be to not let that stop you from learning nd enjoying the game. Buy a tennis racket and a tennis outfit and it if you can afford to do so, purchase a membership to a tennis club and lessons with the best professional tennis pro you can afford. If you are an excellent physical shape and are divinely gifted with PHYSICAL stamina and hand, eye and foot coordination, you might be able to enter the competitions at your tennis club and maybe even advance to local level competitions.
Making the pro tour however, would be nothing short of a miracle. Please however, don't let this advice deter you from picking up the game and having a lot of fun!