So lets give you the quick answer, "no you are not too old". Now I think I should actually re-phrase the question, "Do I want to learn to play a musical instrument?" If you can ask yourself this question, whatever age you are, then you should be able to answer positively.
So let's assume you have retired and you are aged between sixty and seventy years old. Let's also assume you have some saving and a pension and you need a hobby to fill up your time. You decide that you want to learn to play a keyboard instrument. The next step is do you want an electric organ or electric keyboard.
If you want a new electric organ such as the Roland Atelier, its going to cost you anything up to twenty thousand pounds. Having said that, the organ market is all but dead in the UK, so there is a thriving second hand market, and plenty of bargains to be had. If you want an electric keyboard then you can buy one of these, brand new with the latest technology for between two and three thousand pounds. If you do go down the keyboard path then I would recommend you buy an arranger keyboard such as the Yamaha Tyros, Ketron SD5, Roland G70 or the Korg PA 800. Although there is some operational learning with these keyboards, they are designed so you can start playing the thing as soon as you take it out of the box.
Avoid workstation keyboards such as the Yamaha ES7 or the Roland Fantom. These are fantastic keyboards but the learning curve for these machines is very steep and if you are learning to play the keyboard, you don't want to be spending all your time learning how to operate the keyboard. Whatever instrument you choose I recommend, you find yourself a music teacher. If you buy a keyboard or organ from a music shop, they can certainly recommend a local teacher or like many music shops provide keyboard lessons on the premises.
Learning music is about what you personally want to get out of it. You might for instance want to learn to play one piece of music or a book of music or just to see how far you can go. There are no limits. You can learn as much or as little as you personally want.
I have taught many older people that have said, "I wish I had learned to play when I was younger" and "children can learn a lot quicker" and "maybe I won't be able to learn at my age". Yes children will pick things up a little quicker because they have less to think about such as a mortgage, bills, work and many other adult related things that children will never have to think about until they themselves are adults.
Adults of any age, have less time to learn a musical instrument but still have the ability to learn. So if you are a member of the older generation and wondering whether to learn a musical instrument I say absolutely YES go for it and enjoy it. You won't regret it I promise you.