Because teen super heroes are teens. When Impel and Tachyon get together their ages come thru and they like to have fun.
Love how much fun they're having together So are they like best friends?
Not at first. They kinda resented the other for a while. Once they found out how much they had in common (other than the speed), they became damn near inseparable. At least, when not doing heroics. Impel (the one with the purple/gold/white costume) is my OC. Tachyon (the one with the blue/silver/gold costume) is originally my friend 's character (R.I.P.). He gave her to me shortly before he passed.