Theres no restriction when it comes to age when you are engaging into altcoins or any other crypto as long you do have the knowledge to deal with it then you are just fine. Talking about conversion of ETH to BTC would really be just simple.One is localbitcoins but you can still go in other methods if you don't like to use LBC. Just simply convert it into exchange specially on local ones which do operates in your country and just simply transfer it directly into your bank account once converted.