Out of interest what would you say his present resale value is, especially given that the Shite somehow flogged the fuckwomble Solankie for £17m?
Calvert-Lewin is 6 months older than Solanke, so we'll keep that in mind, but their physical peaks should be roughly coincident.
2015/16: In his age 18/19 season on loan from Chelsea at Vitesse, Solanke scored 7 and assisted 1 in 26 first-team appearances. Calvert-Lewin spent the first half of the season on loan at Northampton in League Two, and bagged 8 goals plus 1 assist in 26 appearances; after a January recall, he appeared 9 times for Sheffield United without scoring. Advantage: Solanke, due to difference in leagues, but not by too much.
2016/17: Solanke was on the bench for Chelsea 3 times, once in the league and twice in the league cup. Calvert-Lewin came to Everton, and made the 11 appearances around the ankle injury, scoring his first goal against Hull. Advantage: Calvert-Lewin, in getting meaningful time for a PL side.
2017/18: Solanke moved on a free, makes 27 appearances (6 starts) in all comps, gets 1 assist and 1 goal (that on the final day of the season). Calvert-Lewin makes 44 appearances (24 starts) in all comps, with 8 goals and 7 assists total. Advantage: Calvert-Lewin, again.
2018/19: Solanke doesn't appear at all before the new year and is flogged for 17M, having since made 7 appearances with 1 assist for Bournemouth. Calvert-Lewin has 8 goals plus 2 assists in 34 total appearances. Advantage: Calvert-Lewin, and it's not even close.
Internationally, Solanke does have a longer track record with the England youth sides, which I'll mostly attribute to being in Chelsea's academy. He's got that lone senior cap, which was a very odd decision. And he's been a slightly superior goalscorer and U20 and U21 levels.
Solanke went for 17M+ (granted, in the winter window) after not having made any first-team appearances in 6 months. James Maddison went for ~22M coming from the Championship, and Mitrovic went to Fulham for 18M. Calvert-Lewin will have nearly 100 Everton appearances and hopefully 20 total goals by the end of this season. I'd say he'd be upwards of 30M, given age+goalscoring record in PL+English player premium.
Pay attention to Che Adams and Tammy Abraham this summer. Their valuations ought to give an idea of DCL's--his should be higher.