Did i have the right to be offended?

Generally speaking, I don't think that's an appropriate term to use in a work context at all as it comes across to me as patronising and lacking respect. However, context is incredibly important for all situations like this. Respective ages, whether that terms or terms like it are used regularly by that person or in the workplace generally, the specific circumstances under which it was used here and how it was meant. All of that can make a big difference to whether it was appropriate or not, and if it wasn't, how inappropriate it was. Equally, being offended in and of itself doesn't mean anything. Nothing happens. People do things in life all the time that you won't agree with, both to you and generally. Most of them aren't worthy of a particular reaction at all. If this has bothered you in a work context and it is something that you think you should take further, your employer should have processes for that if you want to use them, or otherwise an informal chat either with the person themselves or a manager should sort it out. But whether that is appropriate will, again, depend on the circumstances of the particular incident.

I told him to **** off! It came across patronising.

why did he say it

A reaction which could range from entirely understandable to a significant overreaction depending on the circumstances. But why are you even asking this question? Are you concerned you overreacted, or concerned about consequences at work for swearing at someone?

Do you have the right to be offended? Yes.

Do I think you are taking what was meant to be a compliment too far? Yes.
Take it as a compliment and move on, I’m assuming this person was relatively older than you and said it as they saw you as someone younger than them or perhaps they know someone roughly the same age as you and say the same thing to them.

Basically, brush it off and forget about it. Easiest thing to do.

I just wanted to know if my reaction was justified. And if what he said was meant to be patronising and degrading.

How is that a compliment? He did look older than me. But the word "goodboy". Is something I would call my neighbours dog. Not another human being, and certainly not a work colleague.

You don't just brush a comment like that under the rug. It's important to stand up for yourself, otherwise they will think these types of comments are okay!

Look, do what you want but all I can say is if you do something or take action against this, it’s going to cause problems between you and your colleagues and given you work with these people, it’s something I’d advise against… as you’ll be doing it for a while and you want as little a hostile environment as possible.

So you want me to apologise to him? I had to speak my mind, otherwise I would have pondered the whole day on why I didn't say anything to him

if you are an adult and another man calls you "goodboy" at work. Would you be offended?