My son (age 15) wears a cassock and surplice when he serves Mass… and he loves it!
AND… he wears dress pants, dress shirt and dress shoes.
This last Sunday, two of the altar servers were girls, about 8 and 9 years old (different parish than where my son serves) and the albs were too short… you could see the torn jeans and the Hannah Montana light-up sneakers (and when I say torn jeans, I mean the INTENTIONALLY torn jeans that sell for upwards of $30… not torn jeans that were the best they could afford from St. Vincent de Paul!) Maybe they figured, who’s going to see the clothes under the albs? but those sneakers flashing Morse code everytime that server moved was a bit distracting!
One parish I attended briefly when I lived out of state was just starting up and they didn’t have vestments for the altar servers… both boys and girls (mostly young teens) were asked to wear a white button-down shirt or blouse (NO t-shirts!) and black or navy blue slacks (for the boys) or skirts (for the girls)–no shorts, no jeans, no skirts above the knee. It was very nice, very respectful and far less distracting than everyday fashions… it was far easier for the younger people to focus on the Mass rather than what their friends were wearing to church that day!