Just what is a Buddha, and who can become one? Well I guess we should quote a Pali-English dictionary first of all before we can discuss the matter further.
Buddha Vacana have an easy to use Pali-English dictionary on line and an option to download it for offline use. In your initial research into Buddhism I would highly recommend bookmarking their site because you will come across numerous Pali words, both within the Suttas and in the commentaries that you will no doubt read. I only wish I had found their site when I started out. It would have made things a lot easier for me.
Anyway; if you type Buddha into the search field, this is what you get:
buddha: [pp. of bujjhati] known; understood; perceived. (m.), one who has attained enlightenment; the Enlightened One. || buḍḍha (adj.) aged; old.
So, a Buddha is one who has attained enlightenment, or is the Enlightened One. There is no mention of supernatural powers, god like features and such stuff. There is only the mention of one who has ‘attained’. To be a little more specific, the one who has attained has done it off their own back. They had no guide, no scripture to work from, no Guru to follow and no path to walk. This is what makes a Buddha so special. They discover the Dhamma, the 4 Noble Truths and the Noble 8 Fold Path without knowing how to discover it in the first place.
There are certainly other persons who attain enlightenment through practicing the Dhamma, and these venerable persons are given the title of Arahant. But they have had a Guru to get advice from, they have had scripture to read and they have had a path to follow. They have reached enlightenment, but they are not Buddhas.
Essentially anyone can become a Buddha, but there is one overriding proviso that stops that from occurring. The Dhamma has to be lost first of all, before another Buddha can arise. If the Dhamma is still known then you can only become an Arahant, not a Buddha, because you have the guidance of a Buddha on how to attain enlightenment and the path on which you must tread. That is not to decry the status of Arahant at all. That level of achievement is almost superhuman in itself, and one that should be applauded and one that we should be grateful for, because if we have an Arahant alive in our times, then we have the best teacher we could wish for.
So don’t be too despondent at the thought that you will not become a Buddha. That happens only once every few thousand years. But becoming an Arahant is perfectly possible, if you apply yourself wholeheartedly for the rest of your life. So get to it… and may you find the peace you are searching for.