>Am I too old to learn it? I mean, I don't want to be a pro or something, I just want to play it for fun, as a hobby.
Not at all.
>How do I begin with it?
Buy a guitar(probably the hardest part for a brohno, but, oh well), amp, picks, strings(the stock ones are usually bad and shouldn't last much). Get Guitar Pro/Powertab, go to sites like 911tabs.com and search for some songs you like and you think must be easy.
There's tons of video tutorials on youtube too, and websites with free resources for learning, google is your friend.
>Is it possible to learn it just by reading tabs and listening to the music?
Depends how exigent you are regarding your performance, but I wouldn't say it's possible anyway. Watching videos(supposing you don't want to get a teacher) and doing specific exercises are strongly recommended, as it's quite easy to develop bad habits with really basic things such as merely picking otherwise.
Now if you mean theoretical knowledge, you don't really need much, if any. But it's really useful, and it's quite pleasant to be able to understand what you're playing.