If you loved your current boyfriend enough that you didn’t have to question whether or not to break up with him, then you would have your answer.
Since your current boyfriend is giving your permission to date the other fellow (I’m only assuming that you would put the first relationship on hold and be one on one with the other guy) then you should probably try it, but not without first letting your friend know that you are about to break up with your boyfriend to give it a go with him. Your friend might not want you to do that (for a whole host of reasons). What I’m saying is, don’t do anything rash, like breaking up with your boyfriend, unless you have a pretty good idea that your friend wants to actually date you and doesn’t just have a little crush.
Also, understand that it might not work out with your friend either, and your current boyfriend may or may not be willing to take you back if you breakup with him, or even if you are dating both of them at the same time (which I don’t recommend). At that point, you may lose 2 good guys.
What exactly is the age difference problem with your current boyfriend? Is it just society’s idea of what constitutes a reasonable age difference, or are there real/uncomfortable differences which you are noticing such as not being in the same place maturity-wise, not being in the same place on the experiences part of your lives (having finished school, finsihed sowing your wild oats, not having the same life goals like getting married or having children)?
If you decide to stay with your current boyfriend, it might be a good idea (even though it will be painful at first, and you might not think necessary) to put some distance, emotion-wise and actual physical distance, between you and your friend. In other words, if you stay with your current fellow, you need to cool it with the buddy, because he is, in fact, coming between you and your current boyfriend and that’s not really nice. I get that you consider the friend to be your best friend, but you and I and the refrigerator know that unless you’re both gay, having friends of the opposite sex is not the same as being best friends with someone of the same sex. There is always going to be some type of sexual tension, even if it’s one sided. But in this case, it’s clearly double sided.
Just some things to think about before you jump into the flames of passion. I wish you all well.