I think you might really scar your old self if you high-fived your old self! You might need to disguise youself to look different!!
Yes, an infinite paradox! Sounds kind of crazy that you would tell yourself how to make a time machine, but your old self would have had to know how to make a time machine in the first place to get you to the past! Crazy!
The paradox would come from who originally told you how to make the time machine. Because if you invent it when you are 60, then go back in time so that your 20 year old self could enjoy the benefits of being young and having a time machine, you would not invent it when you are 60, so you could not go back in time. However, then because you did not go back in time you would now invent it when you are 60 again and so you can now tell you 20 year old self how to build one. Do you see what I’m getting at, there is a reason why time is linear and not circular.