The KWA is a great choice out of the box but not fully compatible with TM and that can be a problem in the futur.
The ICS SIG552 is a good airsoft but Sigs only use Sig mags unless you buy the 556 wich is usually compatible with M4 mags. Special mags can be hard to find and will cost more.
I would stick with an electric airsoft unless you have a big budget for mags and upgraded parts.
Someone mentionned the KA M4A1, I would go for the KA M4 CQB, they are very good buy's for your first airsoft. We cant help you with retailers because of the age thing, but you are paying to much if you buy those airsoft.