1. Can I kick out non active players from my league?
Providing you have made the league rules clear (see example) then it is OK to kick managers who do not comply with these rules. In most leagues people who know they can't be active for a period of time because of a holiday or similar will PM the host to explain the situation and as a result you shouldn't kick them.
2. I’m currently in Elite league, I’m level 15 but with so many 18+ teams I cannot realistically achieve the 6 place target in races, I just seen a million miles behind n terms of car development. Is there anything being done to even the playing field ?
Unfortunately this is partially a result of the myriad of guides that now exist on the forum. Before these guides existed most newcomers spent a few seasons learning the game before they got the success they needed to achieve the dizzy heights of the Elite tier. Now it is not uncommon for managers to promote to Elite after only two seasons and this causes a problem mainly because their Tech Centre is low level and as a result their low power Boost & DRS is a huge handicap.
I'm afraid there is nothing much you can do about it other than enjoy the learning experience and wait until you hit L16 at which point you should start to get good results.
The good news is that you will level up more quickly because the number of XP you receive each race is a function of the difference between your level and that of your high level competitors.