Leodis McKelvin is the oldest cornerback on the Buffalo Bills at age 27, and he’s the only cornerback on the roster with more than two years of NFL experience. “It’s a new role for me, as far as me being the oldest,” McKelvin said after Tuesday’s practice at One Bills Drive. “We’re young but we have guys who have showed they have the ability to take a leadership role by what they do on the field and their playing ability.” The Bills would like to think they are young and talented at cornerback. Buffalo needs some young guys to learn quickly, however, or the cornerback unit will be known as young and dangerously thin. McKelvin and second-year man Stephon Gilmore form the starting duo. Gilmore is coming off an excellent rookie season. McKelvin has been in and out of the lineup over five seasons but earned himself a four-year contract extension from the Bills in February thanks to a capable four-game starting stint late last season. After them? The competition is wide open. The next two on the depth chart are speedy Ron Brooks, a fourth-round pick last year, and Justin Rogers, a seventh-round pick in 2011. After them it’s Crezdon Butler, T.J. Heath, Vernon Kearney, Kip Edwards, Nickell Robey and Jumal Rolle. Never heard of them? Don’t feel bad. Asked about the youth at corner, coach Doug Marrone said: “I like it. I really do because sometimes when you come in and you are teaching new concepts … it is good to get them when they are fresh and they are not locked into a certain technique that they are doing. So I like a lot of those young guys back there.” It was a bit of a surprise the Bills did not draft a cornerback. An ideal time to pick one would have come with the 78th pick, in the third round. But five corners were taken between picks 60 and 71. Buffalo picked the fastest player in the draft, receiver Marquise Goodwin, instead. The Bills’ depth at safety may make the cornerback unit deeper than it appears. Aaron Williams, starting at free safety with Pro Bowler Jairus Byrd unsigned, is a converted corner who could drop down and cover a slot receiver. Rookie fourth-round pick Duke Williams has the ability, the Bills think, to cover slot receivers. Byrd has coverage ability, as well. New defensive coordinator Mike Pettine liked to use a three-safety nickel scheme (with two cornerbacks) at times during his tenure with the New York Jets. Most teams keep six cornerbacks on the roster. McKelvin said it’s important for the Bills’ defensive backs to work together, especially since veteran secondary leader George Wilson left in free agency. “Everybody’s got to take an extra step,” McKelvin said. “There’s not that somebody who’s like George. He was a real big brother for all of us.”