This should get you started:
Select Top 1000000 tblAssets.AssetID,
tblAssets.AssetName,
tsysAssetTypes.AssetTypename,
tblAssetCustom.Manufacturer,
tblAssetCustom.Model,
tblAssetCustom.Serialnumber,
tblAssets.Firstseen,
tblAssets.Lastseen
From tblAssets
Inner Join tblAssetCustom On tblAssetCustom.AssetID = tblAssets.AssetID
Inner Join tsysAssetTypes On tsysAssetTypes.AssetType = tblAssets.Assettype
Where tblAssets.Firstseen < DateAdd(Year, -5, GetDate()) And
tblAssetCustom.State = 1