Will need to become a much better scorer of easy finishes and typical box runs to do so, unless he becomes an amazing finisher from middle-distance.
To tally so high, you need a lot of bread and butter goals: headers, tap-ins, cut across the near post finishes, scrambles.
Rashford is young and learning (yong and lernin), plus we use him so exhaustively away from goal. He would also have to be the main forward (note not striker, as neither Rooney nor Charlton were that for any extended period of their careers) here who wards of any £100m+ challenger for his position on the market. On top of that, he would have to remain relatively injury free, further to that, he'd have to be a mainstay in the side for over a decade.
There's a lot of hurdles there to overcome to get anywhere close to Rooney's record. I don't know if he has the base talent level to match Charlton's record - when Rooney was on the up, it was agreed he had talent to an all-time potential, which nobody has said anything like the same with Rashford, thus far. In looking at the two aforementioned top-scorer holders, you're talking about players who are right at the top of the tree for talent that has ever come out of England with Rooney always being Charlton's natural successor. Rashford really would have to kick on to be in such esteemed company.